From f7b15b5098ee89a2628129fbbef9901bded9d27b Mon Sep 17 00:00:00 2001 From: Peter Eisentraut Date: Sun, 10 Oct 2010 13:46:02 +0300 Subject: [PATCH] Extensive ECPG documentation improvements Satoshi Nagayasu, reviewed and revised by Peter Eisentraut Since this introduces new refentries that we probably don't want to publish as man pages, tweak man page stylesheet to omit man pages without manvolnum element. Peter Eisentraut --- doc/src/sgml/ecpg.sgml | 6683 ++++++++++++++++++++++++------- doc/src/sgml/stylesheet-man.xsl | 44 + 2 files changed, 5327 insertions(+), 1400 deletions(-) diff --git a/doc/src/sgml/ecpg.sgml b/doc/src/sgml/ecpg.sgml index 645a6faafae..835d35ab991 100644 --- a/doc/src/sgml/ecpg.sgml +++ b/doc/src/sgml/ecpg.sgml @@ -13,7 +13,7 @@ Linus Tolke (linus@epact.se) and Michael Meskes (meskes@postgresql.org). Originally it was written to work with C. It also works with C++, but - it does not recognize all C++ constructs yet. + it does not recognize all C++ constructs yet. @@ -28,10 +28,13 @@ An embedded SQL program consists of code written in an ordinary programming language, in this case C, mixed with SQL commands in - specially marked sections. To build the program, the source code + specially marked sections. To build the program, the source code (*.pgc) is first passed through the embedded SQL preprocessor, which converts it - to an ordinary C program, and afterwards it can be processed by a C - compiler. + to an ordinary C program (*.c), and afterwards it can be processed by a C + compiler. (For details about the compiling and linking see ). + Converted ECPG applications call functions in the libpq library + through the embedded SQL library (ecpglib), and communicate with + the PostgreSQL server using the normal frontend-backend protocol. @@ -71,7 +74,15 @@ EXEC SQL ...; - Connecting to the Database Server + Managing Database Connections + + + This section describes how to open, close, and switch database + connections. + + + + Connecting to the database server One connects to a database using the following statement: @@ -200,10 +211,91 @@ EXEC SQL CONNECT TO :target USER :user; example above to encapsulate the connection target string somewhere. - + - - Closing a Connection + + Choosing a connection + + + SQL statements in embedded SQL programs are by default executed on + the current connection, that is, the most recently opened one. If + an application needs to manage multiple connections, then there are + two ways to handle this. + + + + The first option is to explicitly choose a connection for each SQL + statement, for example: + +EXEC SQL AT connection-name SELECT ...; + + This option is particularly suitable if the application needs to + use several connections in mixed order. + + + + If your application uses multiple threads of execution, they cannot share a + connection concurrently. You must either explicitly control access to the connection + (using mutexes) or use a connection for each thread. If each thread uses its own connection, + you will need to use the AT clause to specify which connection the thread will use. + + + + The second option is to execute a statement to switch the current + connection. That statement is: + +EXEC SQL SET CONNECTION connection-name; + + This option is particularly convenient if many statements are to be + executed on the same connection. It is not thread-aware. + + + + Here is an example program managing multiple database connections: + + +EXEC SQL BEGIN DECLARE SECTION; + char dbname[1024]; +EXEC SQL END DECLARE SECTION; + +int +main() +{ + EXEC SQL CONNECT TO testdb1 AS con1 USER testuser; + EXEC SQL CONNECT TO testdb2 AS con2 USER testuser; + EXEC SQL CONNECT TO testdb3 AS con3 USER testuser; + + /* This query would be executed in the last opened database "testdb3". */ + EXEC SQL SELECT current_database() INTO :dbname; + printf("current=%s (should be testdb3)\n", dbname); + + /* Using "AT" to run a query in "testdb2" */ + EXEC SQL AT con2 SELECT current_database() INTO :dbname; + printf("current=%s (should be testdb2)\n", dbname); + + /* Switch the current connection to "testdb1". */ + EXEC SQL SET CONNECTION con1; + + EXEC SQL SELECT current_database() INTO :dbname; + printf("current=%s (should be testdb1)\n", dbname); + + EXEC SQL DISCONNECT ALL; + return 0; +} +]]> + + This example would produce this output: + +current=testdb3 (should be testdb3) +current=testdb2 (should be testdb2) +current=testdb1 (should be testdb1) + + + + + + Closing a connection To close a connection, use the following statement: @@ -247,6 +339,8 @@ EXEC SQL DISCONNECT connection; It is good style that an application always explicitly disconnect from every connection it opened. + + @@ -257,6 +351,9 @@ EXEC SQL DISCONNECT connection; Below are some examples of how to do that. + + Executing SQL statements + Creating a table: @@ -282,6 +379,26 @@ EXEC SQL COMMIT; + + Updates: + +EXEC SQL UPDATE foo + SET ascii = 'foobar' + WHERE number = 9999; +EXEC SQL COMMIT; + + + + + SELECT statements that return a single result + row can also be executed using + EXEC SQL directly. To handle result sets with + multiple rows, an application has to use a cursor; + see below. (As a special case, an + application can fetch multiple rows at once into an array host + variable; see .) + + Single-row select: @@ -289,6 +406,33 @@ EXEC SQL SELECT foo INTO :FooBar FROM table1 WHERE ascii = 'doodad'; + + Also, a configuration parameter can be retreived with the + SHOW command: + +EXEC SQL SHOW search_path INTO :var; + + + + + The tokens of the form + :something are + host variables, that is, they refer to + variables in the C program. They are explained in . + + + + + Using cursors + + + To retrieve a result set holding multiple rows, an application has + to declare a cursor and fetch each row from the cursor. The steps + to use a cursor are the following: declare a cursor, open it, fetch + a row from the cursor, repeat, and finally close it. + + Select using cursors: @@ -304,72 +448,150 @@ EXEC SQL COMMIT; - Updates: - -EXEC SQL UPDATE foo - SET ascii = 'foobar' - WHERE number = 9999; -EXEC SQL COMMIT; - + For more details about declaration of the cursor, + see , and + see for FETCH command + details. - - The tokens of the form - :something are - host variables, that is, they refer to - variables in the C program. They are explained in . - + + + The ECPG DECLARE command does not actually + cause a statement to be sent to the PostgreSQL backend. The + cursor is opened in the backend (using the + backend's DECLARE command) at the point when + the OPEN command is executed. + + + + + + Managing transactions In the default mode, statements are committed only when EXEC SQL COMMIT is issued. The embedded SQL interface also supports autocommit of transactions (similar to - libpq behavior) via the command-line - option to ecpg (see below) or via the EXEC SQL - SET AUTOCOMMIT TO ON statement. In autocommit mode, each - command is automatically committed unless it is inside an explicit - transaction block. This mode can be explicitly turned off using - EXEC SQL SET AUTOCOMMIT TO OFF. - - - - - Choosing a Connection - - - The SQL statements shown in the previous section are executed on - the current connection, that is, the most recently opened one. If - an application needs to manage multiple connections, then there are - two ways to handle this. + libpq behavior) via the + command-line option to ecpg (see ) or via the EXEC SQL SET AUTOCOMMIT TO + ON statement. In autocommit mode, each command is + automatically committed unless it is inside an explicit transaction + block. This mode can be explicitly turned off using EXEC + SQL SET AUTOCOMMIT TO OFF. - - The first option is to explicitly choose a connection for each SQL - statement, for example: + + The following transaction management commands are available: + + + + EXEC SQL COMMIT + + + Commit an in-progress transaction. + + + + + + EXEC SQL ROLLBACK + + + Roll back an in-progress transaction. + + + + + + EXEC SQL SET AUTOCOMMIT TO ON + + + Enable autocommit mode. + + + + + + SET AUTOCOMMIT TO OFF + + + Disable autocommit mode. This is the default. + + + + + + + + + Prepared statements + + + When the values to be passed to an SQL statement are not known at + compile time, or the same statement is going to be used many + times, then prepared statements can be useful. + + + + The statement is prepared using the + command PREPARE. For the values that are not + known yet, use the + placeholder ?: -EXEC SQL AT connection-name SELECT ...; +EXEC SQL PREPARE stmt1 FROM "SELECT oid, datname FROM pg_database WHERE oid = ?"; - This option is particularly suitable if the application needs to - use several connections in mixed order. - + - - If your application uses multiple threads of execution, they cannot share a - connection concurrently. You must either explicitly control access to the connection - (using mutexes) or use a connection for each thread. If each thread uses its own connection, - you will need to use the AT clause to specify which connection the thread will use. - - - - The second option is to execute a statement to switch the current - connection. That statement is: + + If a statement returns a single row, the application can + call EXECUTE after + PREPARE to execute the statement, supplying the + actual values for the placeholders with a USING + clause: -EXEC SQL SET CONNECTION connection-name; +EXEC SQL EXECUTE stmt1 INTO :dboid, :dbname USING 1; - This option is particularly convenient if many statements are to be - executed on the same connection. It is not thread-aware. - + + + + If a statement return multiple rows, the application can use a + cursor declared based on the prepared statement. To bind input + parameters, the cursor must be opened with + a USING clause: + +EXEC SQL PREPARE stmt1 FROM "SELECT oid,datname FROM pg_database WHERE oid > ?"; +EXEC SQL DECLARE foo_bar CURSOR FOR stmt1; + +/* when end of result set reached, break out of while loop */ +EXEC SQL WHENEVER NOT FOUND DO BREAK; + +EXEC SQL OPEN foo_bar USING 100; +... +while (1) +{ + EXEC SQL FETCH NEXT FROM foo_bar INTO :dboid, :dbname; + ... +} +EXEC SQL CLOSE foo_bar; + + + + + When you don't need the prepared statement anymore, you should + deallocate it: + +EXEC SQL DEALLOCATE PREPARE name; + + + + + For more details about PREPARE, + see . Also + see for more details about using + placeholders and input parameters. + + @@ -391,7 +613,13 @@ EXEC SQL SET CONNECTION connection-name; variables. - + + Another way to exchange values between PostgreSQL backends and ECPG + applications is the use of SQL descriptors, described + in . + + + Overview @@ -416,7 +644,7 @@ EXEC SQL INSERT INTO sometable VALUES (:v1, 'foo', :v2); - + Declare Sections @@ -467,107 +695,8 @@ EXEC SQL int i = 4; - - Different types of host variables - - As a host variable you can also use arrays, typedefs, structs and - pointers. Moreover there are special types of host variables that exist - only in ECPG. - - - - A few examples on host variables: - - - Arrays - - - One of the most common uses of an array declaration is probably the - allocation of a char array as in: - -EXEC SQL BEGIN DECLARE SECTION; - char str[50]; -EXEC SQL END DECLARE SECTION; - - Note that you have to take care of the length for yourself. If you use - this host variable as the target variable of a query which returns a - string with more than 49 characters, a buffer overflow occurs. - - - - - - Typedefs - - - Use the typedef keyword to map new types to already - existing types. - -EXEC SQL BEGIN DECLARE SECTION; - typedef char mychartype[40]; - typedef long serial_t; -EXEC SQL END DECLARE SECTION; - - Note that you could also use: - -EXEC SQL TYPE serial_t IS long; - - This declaration does not need to be part of a declare section. - - - - - - Pointers - - - You can declare pointers to the most common types. Note however that - you cannot use pointers as target variables of queries without - auto-allocation. See for more - information on auto-allocation. - - -EXEC SQL BEGIN DECLARE SECTION; - int *intp; - char **charp; -EXEC SQL END DECLARE SECTION; - - - - - - Special types of variables - - - ECPG contains some special types that help you to interact easily with - data from the SQL server. For example it has implemented support for - the varchar, numeric, date, timestamp, and interval types. - contains basic functions to deal with - those types, such that you do not need to send a query to the SQL - server just for adding an interval to a timestamp for example. - - - The special type VARCHAR - is converted into a named struct for every variable. A - declaration like: - -VARCHAR var[180]; - - is converted into: - -struct varchar_var { int len; char arr[180]; } var; - - This structure is suitable for interfacing with SQL datums of type - varchar. - - - - - - - - - <command>SELECT INTO</command> and <command>FETCH INTO</command> + + Retrieving query results Now you should be able to pass data generated by your program into @@ -577,6 +706,9 @@ struct varchar_var { int len; char arr[180]; } var; FETCH. These commands have a special INTO clause that specifies which host variables the retrieved values are to be stored in. + SELECT is used for a query that returns only + single row, and FETCH is used for a query that + returns multiple rows, using a cursor. @@ -617,7 +749,8 @@ EXEC SQL DECLARE foo CURSOR FOR SELECT a, b FROM test; ... -do { +do +{ ... EXEC SQL FETCH NEXT FROM foo INTO :v1, :v2; ... @@ -634,7 +767,951 @@ do { - + + Type mapping + + + When ECPG applications exchange values between the PostgreSQL + server and the C application, such as when retrieving query + results from the server or executing SQL statements with input + parameters, the values need to be converted between PostgreSQL + data types and host language variable types (C language data + types, concretely). One of the main points of ECPG is that it + takes care of this automatically in most cases. + + + + In this respect, there are two kinds of data types: Some simple + PostgreSQL data types, such as integer + and text, can be read and written by the application + directly. Other PostgreSQL data types, such + as timestamp and numeric can only be + accessed through special library functions; see + . + + + + shows which PostgreSQL + data types correspond to which C data types. When you wish to + send or receive a value of a given PostgreSQL data type, you + should declare a C variable of the corresponding C data type in + the declare section. + + + + Mapping between PostgreSQL data types and C variable types + + + + PostgreSQL data type + Host variable type + + + + + + smallint + short + + + + integer + int + + + + bigint + long long int + + + + decimal + decimalThis type can only be accessed through special library functions; see . + + + + numeric + numeric + + + + real + float + + + + double precision + double + + + + serial + int + + + + bigserial + long long int + + + + oid + unsigned int + + + + character(n), varchar(n), text + char[n+1], VARCHAR[n+1]declared in ecpglib.h + + + + name + char[NAMEDATALEN] + + + + timestamp + timestamp + + + + interval + interval + + + + date + date + + + + boolean + booldeclared in ecpglib.h if not native + + + +
+ + + Handling character strings + + + To handle SQL character string data types, such + as varchar and text, there are two + possible ways to declare the host variables. + + + + One way is using char[], an array + of char, which is the most common way to handle + character data in C. + +EXEC SQL BEGIN DECLARE SECTION; + char str[50]; +EXEC SQL END DECLARE SECTION; + + Note that you have to take care of the length yourself. If you + use this host variable as the target variable of a query which + returns a string with more than 49 characters, a buffer overflow + occurs. + + + + The other way is using the VARCHAR type, which is a + special type provided by ECPG. The definition on an array of + type VARCHAR is converted into a + named struct for every variable. A declaration like: + +VARCHAR var[180]; + + is converted into: + +struct varchar_var { int len; char arr[180]; } var; + + The member arr hosts the string + including a terminating zero byte. Thus, to store a string in + a VARCHAR host variable, the host variable has to be + declared with the length including the zero byte terminator. The + member len holds the length of the + string stored in the arr without the + terminating zero byte. When a host variable is used as input for + a query, if strlen(arr) + and len are different, the shorter one + is used. + + + + Two or more VARCHAR host variables cannot be defined + in single line statement. The following code will confuse + the ecpg preprocessor: + +VARCHAR v1[128], v2[128]; /* WRONG */ + + Two variables should be defined in separate statements like this: + +VARCHAR v1[128]; +VARCHAR v2[128]; + + + + + VARCHAR can be written in upper or lower case, but + not in mixed case. + + + + char and VARCHAR host variables can + also hold values of other SQL types, which will be stored in + their string forms. + + + + + Accessing special data types + + + ECPG contains some special types that help you to interact easily + with some special data types from the PostgreSQL server. In + particular, it has implemented support for the + numeric, decimal, date, timestamp, + and interval types. These data types cannot usefully be + mapped to primitive host variable types (such + as int, long long int, + or char[]), because they have a complex internal + structure. Applications deal with these types by declaring host + variables in special types and accessing them using functions in + the pgtypes library. The pgtypes library, described in detail + in contains basic functions to deal + with those types, such that you do not need to send a query to + the SQL server just for adding an interval to a timestamp for + example. + + + + The follow subsections describe these special data types. For + more details about pgtypes library functions, + see . + + + + timestamp, date + + + Here is a pattern for handling timestamp variables + in the ECPG host application. + + + + First, the program has to include the header file for the + timestamp type: + +#include <pgtypes_timestamp.h> + + + + + Next, declare a host variable as type timestamp in + the declare section: + +EXEC SQL BEGIN DECLARE SECTION; +timestamp ts; +EXEC SQL END DECLARE SECTION; + + + + + And after reading a value into the host variable, process it + using pgtypes library functions. In following example, the + timestamp value is converted into text (ASCII) form + with the PGTYPEStimestamp_to_asc() + function: + +EXEC SQL SELECT now()::timestamp INTO :ts; + +printf("ts = %s\n", PGTYPEStimestamp_to_asc(ts)); + + This example will show some result like following: + +ts = 2010-06-27 18:03:56.949343 + + + + + In addition, the DATE type can be handled in the same way. The + program has to include pg_types_date.h, declare a host variable + as the date type and convert a DATE value into a text form using + PGTYPESdate_to_asc() function. For more details about the + pgtypes library functions, see . + + + + + interval + + + The handling of the interval type is also similar + to the timestamp and date types. It + is required, however, to allocate memory for + an interval type value explicitly. In other words, + the memory space for the variable has to be allocated in the + heap memory, not in the stack memory. + + + + Here is an example program: + +#include <stdio.h> +#include <stdlib.h> +#include <pgtypes_interval.h> + +int +main(void) +{ +EXEC SQL BEGIN DECLARE SECTION; + interval *in; +EXEC SQL END DECLARE SECTION; + + EXEC SQL CONNECT TO testdb; + + in = PGTYPESinterval_new(); + EXEC SQL SELECT '1 min'::interval INTO :in; + printf("interval = %s\n", PGTYPESinterval_to_asc(in)); + PGTYPESinterval_free(in); + + EXEC SQL COMMIT; + EXEC SQL DISCONNECT ALL; + return 0; +} + + + + + + numeric, decimal + + + The handling of the numeric + and decimal types is similar to the + interval type: It requires defining a pointer, + allocating some memory space on the heap, and accessing the + variable using the pgtypes library functions. For more details + about the pgtypes library functions, + see . + + + + No functions are provided specifically for + the decimal type. An application has to convert it + to a numeric variable using a pgtypes library + function to do further processing. + + + + Here is an example program handling numeric + and decimal type variables. + +#include <stdio.h> +#include <stdlib.h> +#include <pgtypes_numeric.h> + +EXEC SQL WHENEVER SQLERROR STOP; + +int +main(void) +{ +EXEC SQL BEGIN DECLARE SECTION; + numeric *num; + numeric *num2; + decimal *dec; +EXEC SQL END DECLARE SECTION; + + EXEC SQL CONNECT TO testdb; + + num = PGTYPESnumeric_new(); + dec = PGTYPESdecimal_new(); + + EXEC SQL SELECT 12.345::numeric(4,2), 23.456::decimal(4,2) INTO :num, :dec; + + printf("numeric = %s\n", PGTYPESnumeric_to_asc(num, 0)); + printf("numeric = %s\n", PGTYPESnumeric_to_asc(num, 1)); + printf("numeric = %s\n", PGTYPESnumeric_to_asc(num, 2)); + + /* Convert decimal to numeric to show a decimal value. */ + num2 = PGTYPESnumeric_new(); + PGTYPESnumeric_from_decimal(dec, num2); + + printf("decimal = %s\n", PGTYPESnumeric_to_asc(num2, 0)); + printf("decimal = %s\n", PGTYPESnumeric_to_asc(num2, 1)); + printf("decimal = %s\n", PGTYPESnumeric_to_asc(num2, 2)); + + PGTYPESnumeric_free(num2); + PGTYPESdecimal_free(dec); + PGTYPESnumeric_free(num); + + EXEC SQL COMMIT; + EXEC SQL DISCONNECT ALL; + return 0; +} + + + + + + + Host variables with nonprimitive types + + + As a host variable you can also use arrays, typedefs, structs, and + pointers. + + + + Arrays + + + There are two use cases for arrays as host variables. The first + is a way to store some text string in char[] + or VARCHAR[], as + explained . The second use case is to + retreive multiple rows from a query result without using a + cursor. Without an array, to process a query result consisting + of multiple rows, it is required to use a cursor and + the FETCH command. But with array host + variables, multiple rows can be received at once. The length of + the array has to be defined to be able to accomodate all rows, + otherwise a buffer overflow will likely occur. + + + + Following example scans the pg_database + system table and shows all OIDs and names of the available + databases: + +int +main(void) +{ +EXEC SQL BEGIN DECLARE SECTION; + int dbid[8]; + char dbname[8][16]; + int i; +EXEC SQL END DECLARE SECTION; + + memset(dbname, 0, sizeof(char)* 16 * 8); + memset(dbid, 0, sizeof(int) * 8); + + EXEC SQL CONNECT TO testdb; + + /* Retrieve multiple rows into arrays at once. */ + EXEC SQL SELECT oid,datname INTO :dbid, :dbname FROM pg_database; + + for (i = 0; i < 8; i++) + printf("oid=%d, dbname=%s\n", dbid[i], dbname[i]); + + EXEC SQL COMMIT; + EXEC SQL DISCONNECT ALL; + return 0; +} + + + This example shows following result. (The exact values depend on + local circumstances.) + +oid=1, dbname=template1 +oid=11510, dbname=template0 +oid=11511, dbname=postgres +oid=313780, dbname=testdb +oid=0, dbname= +oid=0, dbname= +oid=0, dbname= + + + + + + Structures + + + A structure whose member names match the column names of a query + result, can be used to retrieve multiple columns at once. The + structure enables handling multiple column values in a single + host variable. + + + + The following example retrieves OIDs, names, and sizes of the + avilable databases from the pg_database + system table and using + the pg_database_size() function. In this + example, a structure variable dbinfo_t with + members whose names match each column in + the SELECT result is used to retrieve one + result row without putting multiple host variables in + the FETCH statement. + +EXEC SQL BEGIN DECLARE SECTION; + typedef struct + { + int oid; + char datname[65]; + long long int size; + } dbinfo_t; + + dbinfo_t dbval; +EXEC SQL END DECLARE SECTION; + + memset(&dbval, 0, sizeof(dbinfo_t)); + + EXEC SQL DECLARE cur1 CURSOR FOR SELECT oid, datname, pg_database_size(oid) AS size FROM pg_database; + EXEC SQL OPEN cur1; + + /* when end of result set reached, break out of while loop */ + EXEC SQL WHENEVER NOT FOUND DO BREAK; + + while (1) + { + /* Fetch multiple columns into one structure. */ + EXEC SQL FETCH FROM cur1 INTO :dbval; + + /* Print members of the structure. */ + printf("oid=%d, datname=%s, size=%lld\n", dbval.oid, dbval.datname, dbval.size); + } + + EXEC SQL CLOSE cur1; + + + + + This example shows following result. (The exact values depend on + local circumstances.) + +oid=1, datname=template1, size=4324580 +oid=11510, datname=template0, size=4243460 +oid=11511, datname=postgres, size=4324580 +oid=313780, datname=testdb, size=8183012 + + + + + Structure host variables absorb as many columns + as the structure as fields. Additional columns can be assigned + to other host variables. For example, the above program could + also be restructured like this, with the size + variable outside the structure: + +EXEC SQL BEGIN DECLARE SECTION; + typedef struct + { + int oid; + char datname[65]; + } dbinfo_t; + + dbinfo_t dbval; + long long int size; +EXEC SQL END DECLARE SECTION; + + memset(&dbval, 0, sizeof(dbinfo_t)); + + EXEC SQL DECLARE cur1 CURSOR FOR SELECT oid, datname, pg_database_size(oid) AS size FROM pg_database; + EXEC SQL OPEN cur1; + + /* when end of result set reached, break out of while loop */ + EXEC SQL WHENEVER NOT FOUND DO BREAK; + + while (1) + { + /* Fetch multiple columns into one structure. */ + EXEC SQL FETCH FROM cur1 INTO :dbval, :size; + + /* Print members of the structure. */ + printf("oid=%d, datname=%s, size=%lld\n", dbval.oid, dbval.datname, size); + } + + EXEC SQL CLOSE cur1; + + + + + + Typedefs + + + Use the typedef keyword to map new types to already + existing types. + +EXEC SQL BEGIN DECLARE SECTION; + typedef char mychartype[40]; + typedef long serial_t; +EXEC SQL END DECLARE SECTION; + + Note that you could also use: + +EXEC SQL TYPE serial_t IS long; + + This declaration does not need to be part of a declare section. + + + + + Pointers + + + You can declare pointers to the most common types. Note however + that you cannot use pointers as target variables of queries + without auto-allocation. See + for more information on auto-allocation. + + + + +EXEC SQL BEGIN DECLARE SECTION; + int *intp; + char **charp; +EXEC SQL END DECLARE SECTION; + + + + + + + + Handling nonprimitive SQL data types + + + This section contains information on how to handle nonscalar and + user-defined SQL-level data types in ECPG applications. Note that + this is distinct from the handling of host variables of + nonprimitive types, described in the previous section. + + + + Arrays + + + SQL-level arrays are not directly supported in ECPG. It is not + possible to simply map an SQL array into a C array host variable. + This will result in undefined behavior. Some workarounds exist, + however. + + + + If a query accesses elements of an array + separately, then this avoids the use of arrays in ECPG. Then, a + host variable with a type that can be mapped to the element type + should be used. For example, if a column type is array of + integer, a host variable of type int + can be used. Also if the element type is varchar + or text, a host variable of type char[] + or VARCHAR[] can be used. + + + + Here is an example. Assume the following table: + +CREATE TABLE t3 ( + ii integer[] +); + +testdb=> SELECT * FROM t3; + ii +------------- + {1,2,3,4,5} +(1 row) + + + The following example program retrieves the 4th element of the + array and stores it into a host variable of + type int: + +EXEC SQL BEGIN DECLARE SECTION; +int ii; +EXEC SQL END DECLARE SECTION; + +EXEC SQL DECLARE cur1 CURSOR FOR SELECT ii[4] FROM t3; +EXEC SQL OPEN cur1; + +EXEC SQL WHENEVER NOT FOUND DO BREAK; + +while (1) +{ + EXEC SQL FETCH FROM cur1 INTO :ii ; + printf("ii=%d\n", ii); +} + +EXEC SQL CLOSE cur1; + + + This example shows the following result: + +ii=4 + + + + + To map multiple array elements to the multiple elements in an + array type host variables each element of array column and each + element of the host variable array have to be managed separately, + for example: + +EXEC SQL BEGIN DECLARE SECTION; +int ii_a[8]; +EXEC SQL END DECLARE SECTION; + +EXEC SQL DECLARE cur1 CURSOR FOR SELECT ii[1], ii[2], ii[3], ii[4] FROM t3; +EXEC SQL OPEN cur1; + +EXEC SQL WHENEVER NOT FOUND DO BREAK; + +while (1) +{ + EXEC SQL FETCH FROM cur1 INTO :ii_a[0], :ii_a[1], :ii_a[2], :ii_a[3]; + ... +} + + + + + Note again that + +EXEC SQL BEGIN DECLARE SECTION; +int ii_a[8]; +EXEC SQL END DECLARE SECTION; + +EXEC SQL DECLARE cur1 CURSOR FOR SELECT ii FROM t3; +EXEC SQL OPEN cur1; + +EXEC SQL WHENEVER NOT FOUND DO BREAK; + +while (1) +{ + /* WRONG */ + EXEC SQL FETCH FROM cur1 INTO :ii_a; + ... +} + + would not work correctly in this case, because you cannot map an + array type column to an array host variable directly. + + + + Another workaround is to store arrays in their external string + representation in host variables of type char[] + or VARCHAR[]. For more details about this + representation, see . Note that + this means that the array cannot be accessed naturally as an + array in the host program (without further processing that parses + the text representation). + + + + + Composite types + + + Composite types are not directly supported in ECPG, but an easy workaround is possible. + The + available workarounds are similar to the ones described for + arrays above: Either access each attribute separately or use the + external string representation. + + + + For the following examples, assume the following type and table: + +CREATE TYPE comp_t AS (intval integer, textval varchar(32)); +CREATE TABLE t4 (compval comp_t); +INSERT INTO t4 VALUES ( (256, 'PostgreSQL') ); + + + The most obvious solution is to access each attribute separately. + The following program retrieves data from the example table by + selecting each attribute of the type comp_t + separately: + +EXEC SQL BEGIN DECLARE SECTION; +int intval; +varchar textval[33]; +EXEC SQL END DECLARE SECTION; + +/* Put each element of the composite type column in the SELECT list. */ +EXEC SQL DECLARE cur1 CURSOR FOR SELECT (compval).intval, (compval).textval FROM t4; +EXEC SQL OPEN cur1; + +EXEC SQL WHENEVER NOT FOUND DO BREAK; + +while (1) +{ + /* Fetch each element of the composite type column into host variables. */ + EXEC SQL FETCH FROM cur1 INTO :intval, :textval; + + printf("intval=%d, textval=%s\n", intval, textval.arr); +} + +EXEC SQL CLOSE cur1; + + + + + To enhance this example, the host variables to store values in + the FETCH command can be gathered into one + structure. For more details about the host variable in the + structure form, see . + To switch to the structure, the example can be modified as below. + The two host variables, intval + and textval, become members of + the comp_t structure, and the structure + is specified on the FETCH command. + +EXEC SQL BEGIN DECLARE SECTION; +typedef struct +{ + int intval; + varchar textval[33]; +} comp_t; + +comp_t compval; +EXEC SQL END DECLARE SECTION; + +/* Put each element of the composite type column in the SELECT list. */ +EXEC SQL DECLARE cur1 CURSOR FOR SELECT (compval).intval, (compval).textval FROM t4; +EXEC SQL OPEN cur1; + +EXEC SQL WHENEVER NOT FOUND DO BREAK; + +while (1) +{ + /* Put all values in the SELECT list into one structure. */ + EXEC SQL FETCH FROM cur1 INTO :compval; + + printf("intval=%d, textval=%s\n", compval.intval, compval.textval.arr); +} + +EXEC SQL CLOSE cur1; + + + Although a structure is used in the FETCH + command, the attribute names in the SELECT + clause are specified one by one. This can be enhanced by using + a * to ask for all attributes of the composite + type value. + +... +EXEC SQL DECLARE cur1 CURSOR FOR SELECT (compval).* FROM t4; +EXEC SQL OPEN cur1; + +EXEC SQL WHENEVER NOT FOUND DO BREAK; + +while (1) +{ + /* Put all values in the SELECT list into one structure. */ + EXEC SQL FETCH FROM cur1 INTO :compval; + + printf("intval=%d, textval=%s\n", compval.intval, compval.textval.arr); +} +... + + This way, composite types can be mapped into structures almost + seamlessly, even though ECPG does not understand the composite + type itself. + + + + Finally, it is also possible to store composite type values in + their external string representation in host variables of + type char[] or VARCHAR[]. But that + way, it is not easily possible to access the fields of the value + from the host program. + + + + + User-defined base types + + + New user-defined base types are not directly supported by ECPG. + You can use the external string representation and host variables + of type char[] or VARCHAR[], and this + solution is indeed appropriate and sufficient for many types. + + + + Here is an example using the data type complex from + the example in . The external string + representation of that type is (%lf,%lf), + which is defined in the + functions complex_in() + and complex_out() functions + in . The following example inserts the + complex type values (1,1) + and (3,3) into the + columns a and b, and select + them from the table after that. + + +EXEC SQL BEGIN DECLARE SECTION; + varchar a[64]; + varchar b[64]; +EXEC SQL END DECLARE SECTION; + + EXEC SQL INSERT INTO test_complex VALUES ('(1,1)', '(3,3)'); + + EXEC SQL DECLARE cur1 CURSOR FOR SELECT a, b FROM test_complex; + EXEC SQL OPEN cur1; + + EXEC SQL WHENEVER NOT FOUND DO BREAK; + + while (1) + { + EXEC SQL FETCH FROM cur1 INTO :a, :b; + printf("a=%s, b=%s\n", a.arr, b.arr); + } + + EXEC SQL CLOSE cur1; + + + This example shows following result: + +a=(1,1), b=(3,3) + + + + + Another workaround is avoiding the direct use of the user-defined + types in ECPG and instead create a function or cast that converts + between the user-defined type and a primitive type that ECPG can + handle. Note, however, that type casts, especially implicit + ones, should be introduced into the type system very carefully. + + + + For example, + +CREATE FUNCTION create_complex(r double, i double) RETURNS complex +LANGUAGE SQL +IMMUTABLE +AS $$ SELECT $1 * complex '(1,0')' + $2 * complex '(0,1)' $$; + + After this definition, the following + +EXEC SQL BEGIN DECLARE SECTION; +double a, b, c, d; +EXEC SQL END DECLARE SECTION; + +a = 1; +b = 2; +c = 3; +d = 4; + +EXEC SQL INSERT INTO test_complex VALUES (create_complex(:a, :b), create_complex(:c, :d)); + + has the same effect as + +EXEC SQL INSERT INTO test_complex VALUES ('(1,2)', '(3,4)'); + + + + + + Indicators @@ -668,6 +1745,16 @@ EXEC SQL SELECT b INTO :val :val_ind FROM test1; positive, it means that the value is not null, but it was truncated when it was stored in the host variable. + + + If the argument -r no_indicator is passed to + the preprocessor ecpg, it works in + no-indicator mode. In no-indicator mode, if no + indicator variable is specified, null values are signaled (on + input and output) for character string types as empty string and + for integer types as the lowest possible value for type (for + example, INT_MIN for int). + @@ -684,9 +1771,12 @@ EXEC SQL SELECT b INTO :val :val_ind FROM test1; provide in a string variable. - - The simplest way to execute an arbitrary SQL statement is to use - the command EXECUTE IMMEDIATE. For example: + + Executing statements without a result set + + + The simplest way to execute an arbitrary SQL statement is to use + the command EXECUTE IMMEDIATE. For example: EXEC SQL BEGIN DECLARE SECTION; const char *stmt = "CREATE TABLE test1 (...);"; @@ -694,18 +1784,26 @@ EXEC SQL END DECLARE SECTION; EXEC SQL EXECUTE IMMEDIATE :stmt; - You cannot execute statements that retrieve data (e.g., - SELECT) this way. - + EXECUTE IMMEDIATE can be used for SQL + statements that do not return a result set (e.g., + DDL, INSERT, UPDATE, + DELETE). You cannot execute statements that + retrieve data (e.g., SELECT) this way. The + next section describes how to do that. + + - - A more powerful way to execute arbitrary SQL statements is to - prepare them once and execute the prepared statement as often as - you like. It is also possible to prepare a generalized version of - a statement and then execute specific versions of it by - substituting parameters. When preparing the statement, write - question marks where you want to substitute parameters later. For - example: + + Executing a statement with input parameters + + + A more powerful way to execute arbitrary SQL statements is to + prepare them once and execute the prepared statement as often as + you like. It is also possible to prepare a generalized version of + a statement and then execute specific versions of it by + substituting parameters. When preparing the statement, write + question marks where you want to substitute parameters later. For + example: EXEC SQL BEGIN DECLARE SECTION; const char *stmt = "INSERT INTO test1 VALUES(?, ?);"; @@ -715,34 +1813,78 @@ EXEC SQL PREPARE mystmt FROM :stmt; ... EXEC SQL EXECUTE mystmt USING 42, 'foobar'; - If the statement you are executing returns values, then add an - INTO clause: + + + + When you don't need the prepared statement anymore, you should + deallocate it: + +EXEC SQL DEALLOCATE PREPARE name; + + + + + + Executing a statement with a result set + + + To execute an SQL statement with a single result row, + EXECUTE can be used. To save the result, add + an INTO clause. ?"; int v1, v2; -VARCHAR v3; +VARCHAR v3[50]; EXEC SQL END DECLARE SECTION; EXEC SQL PREPARE mystmt FROM :stmt; ... -EXEC SQL EXECUTE mystmt INTO v1, v2, v3 USING 37; +EXEC SQL EXECUTE mystmt INTO :v1, :v2, :v3 USING 37; ]]> - An EXECUTE command can have an - INTO clause, a USING clause, - both, or neither. - + An EXECUTE command can have an + INTO clause, a USING clause, + both, or neither. + - - When you don't need the prepared statement anymore, you should - deallocate it: + + If a query is expected to return more than one result row, a + cursor should be used, as in the following example. + (See for more details about the + cursor.) -EXEC SQL DEALLOCATE PREPARE name; - - - +EXEC SQL BEGIN DECLARE SECTION; +char dbaname[128]; +char datname[128]; +char *stmt = "SELECT u.usename as dbaname, d.datname " + " FROM pg_database d, pg_user u " + " WHERE d.datdba = u.usesysid"; +EXEC SQL END DECLARE SECTION; +EXEC SQL CONNECT TO testdb AS con1 USER testuser; + +EXEC SQL PREPARE stmt1 FROM :stmt; + +EXEC SQL DECLARE cursor1 CURSOR FOR stmt1; +EXEC SQL OPEN cursor1; + +EXEC SQL WHENEVER NOT FOUND DO BREAK; + +while (1) +{ + EXEC SQL FETCH cursor1 INTO :dbaname,:datname; + printf("dbaname=%s, datname=%s\n", dbaname, datname); +} + +EXEC SQL CLOSE cursor1; + +EXEC SQL COMMIT; +EXEC SQL DISCONNECT ALL; + + + + pgtypes library @@ -771,7 +1913,7 @@ free(out); - + The numeric type The numeric type offers to do calculations with arbitrary precision. See @@ -1094,7 +2236,7 @@ int PGTYPESnumeric_from_decimal(decimal *src, numeric *dst); - + The date type The date type in C enables your programs to deal with data of the SQL type @@ -1570,8 +2712,8 @@ int PGTYPESdate_defmt_asc(date *d, char *fmt, char *str); - - + + The timestamp type The timestamp type in C enables your programs to deal with data of the SQL @@ -2101,7 +3243,7 @@ int PGTYPEStimestamp_sub_interval(timestamp *tin, interval *span, timestamp *tou - + The interval type The interval type in C enables your programs to deal with data of the SQL @@ -2188,7 +3330,7 @@ int PGTYPESinterval_copy(interval *intvlsrc, interval *intvldest); - + The decimal type The decimal type is similar to the numeric type. However it is limited to @@ -2231,8 +3373,8 @@ void PGTYPESdecimal_free(decimal *var); - - + + errno values of pgtypeslib @@ -2281,7 +3423,8 @@ void PGTYPESdecimal_free(decimal *var); PGTYPES_DATE_BAD_DATE - + An invalid date string was passed to + the PGTYPESdate_from_asc function. @@ -2290,7 +3433,8 @@ void PGTYPESdecimal_free(decimal *var); PGTYPES_DATE_ERR_EARGS - + Invalid arguments were passed to the + PGTYPESdate_defmt_asc function. @@ -2299,7 +3443,8 @@ void PGTYPESdecimal_free(decimal *var); PGTYPES_DATE_ERR_ENOSHORTDATE - + An invalid token in the input string was found by the + PGTYPESdate_defmt_asc function. @@ -2308,7 +3453,10 @@ void PGTYPESdecimal_free(decimal *var); PGTYPES_INTVL_BAD_INTERVAL - + An invalid interval string was passed to the + PGTYPESinterval_from_asc function, or an + invalid interval value was passed to the + PGTYPESinterval_to_asc function. @@ -2317,7 +3465,8 @@ void PGTYPESdecimal_free(decimal *var); PGTYPES_DATE_ERR_ENOTDMY - + There was a mismatch in the day/month/year assignment in the + PGTYPESdate_defmt_asc function. @@ -2326,7 +3475,8 @@ void PGTYPESdecimal_free(decimal *var); PGTYPES_DATE_BAD_DAY - + An invalid day of the month value was found by + the PGTYPESdate_defmt_asc function. @@ -2335,7 +3485,8 @@ void PGTYPESdecimal_free(decimal *var); PGTYPES_DATE_BAD_MONTH - + An invalid month value was found by + the PGTYPESdate_defmt_asc function. @@ -2344,7 +3495,20 @@ void PGTYPESdecimal_free(decimal *var); PGTYPES_TS_BAD_TIMESTAMP - + An invalid timestamp string pass passed to + the PGTYPEStimestamp_from_asc function, + or an invalid timestamp value was passed to + the PGTYPEStimestamp_to_asc function. + + + + + + PGTYPES_TS_ERR_EINFTIME + + + An infinite timestamp value was encountered in a context that + cannot handle it. @@ -2352,7 +3516,7 @@ void PGTYPESdecimal_free(decimal *var); - + Special constants of pgtypeslib @@ -2394,7 +3558,7 @@ void PGTYPESdecimal_free(decimal *var); - Named SQL Descriptor Areas + Named SQL descriptor areas A named SQL descriptor area consists of a header, which contains @@ -2430,7 +3594,7 @@ EXEC SQL FETCH NEXT FROM mycursor INTO SQL DESCRIPTOR mydesc; For not yet executed prepared queries, the DESCRIBE statement can be used to get the metadata of the result set: - + EXEC SQL BEGIN DECLARE SECTION; char *sql_stmt = "SELECT * FROM table1"; EXEC SQL END DECLARE SECTION; @@ -2445,7 +3609,7 @@ EXEC SQL DESCRIBE stmt1 INTO SQL DESCRIPTOR mydesc; so using DESCRIPTOR and SQL DESCRIPTOR produced named SQL Descriptor Areas. Now it is mandatory, omitting the SQL keyword produces SQLDA Descriptor Areas, - see . + see . @@ -2499,7 +3663,13 @@ EXEC SQL GET DESCRIPTOR name VALUE numDATETIME_INTERVAL_CODE (integer) - ? + When TYPE is 9, + DATETIME_INTERVAL_CODE will have a value of + 1 for DATE, + 2 for TIME, + 3 for TIMESTAMP, + 4 for TIME WITH TIME ZONE, or + 5 for TIMESTAMP WITH TIME ZONE. @@ -2646,7 +3816,7 @@ EXEC SQL GET DESCRIPTOR mydesc VALUE 1 :id = DATA; - SQLDA Descriptor Areas + SQLDA descriptor areas An SQLDA Descriptor Area is a C language structure which can be also used @@ -2668,56 +3838,80 @@ EXEC SQL DESCRIBE prepared_statement INTO mysqlda; - - The structure of SQLDA is: + + + The general flow of a program that uses SQLDA is: + + Prepare a query, and declare a cursor for it. + Declare an SQLDA for the result rows. + Declare an SQLDA for the input parameters, and initialize them (memory allocation, parameter settings). + Open a cursor with the input SQLDA. + Fetch rows from the cursor, and store them into an output SQLDA. + Read values from the output SQLDA into the host variables (with conversion if necessary). + Close the cursor. + Free the memory area allocated for the input SQLDA. + + + + SQLDA data structure + + + SQLDA uses three data structure + types: sqlda_t, sqlvar_t, + and struct sqlname. + + + + + PostgreSQL's SQLDA has a similar data structure to the one in + IBM DB2 Universal Database, so some technical information on + DB2's SQLDA could help understanding PostgreSQL's one better. + + + + + sqlda_t structure + + + The structure type sqlda_t is the type of the + actual SQLDA. It holds one record. And two or + more sqlda_t structures can be connected in a + linked list with the pointer in + the desc_next field, thus + representing an ordered collection of rows. So, when two or + more rows are fetched, the application can read them by + following the desc_next pointer in + each sqlda_t node. + + + + The definition of sqlda_t is: -#define NAMEDATALEN 64 - -struct sqlname -{ - short length; - char data[NAMEDATALEN]; -}; - -struct sqlvar_struct -{ - short sqltype; - short sqllen; - char *sqldata; - short *sqlind; - struct sqlname sqlname; -}; - struct sqlda_struct { - char sqldaid[8]; - long sqldabc; - short sqln; - short sqld; - struct sqlda_struct *desc_next; - struct sqlvar_struct sqlvar[1]; + char sqldaid[8]; + long sqldabc; + short sqln; + short sqld; + struct sqlda_struct *desc_next; + struct sqlvar_struct sqlvar[1]; }; -typedef struct sqlvar_struct sqlvar_t; -typedef struct sqlda_struct sqlda_t; +typedef struct sqlda_struct sqlda_t; - - - The allocated data for an SQLDA structure is variable as it depends on the - number of fields in a result set and also depends on the length of the string - data values in a record. The individual fields of the SQLDA - structure are: + The meaning of the fields is: sqldaid - It contains the "SQLDA " literal string. + It contains the literal string "SQLDA ". + sqldabc @@ -2726,6 +3920,7 @@ typedef struct sqlda_struct sqlda_t; + sqln @@ -2740,6 +3935,7 @@ typedef struct sqlda_struct sqlda_t; + sqld @@ -2748,6 +3944,7 @@ typedef struct sqlda_struct sqlda_t; + desc_next @@ -2761,15 +3958,43 @@ typedef struct sqlda_struct sqlda_t; sqlvar - This is the array of the fields in the result set. The fields are: + This is the array of the columns in the result set. + + + + + + + + + sqlvar_t structure + + + The structure type sqlvar_t holds a column value + and metadata such as type and length. The definition of the type + is: + + +struct sqlvar_struct +{ + short sqltype; + short sqllen; + char *sqldata; + short *sqlind; + struct sqlname sqlname; +}; + +typedef struct sqlvar_struct sqlvar_t; + + + The meaning of the fields is: - sqltype - It contains the type identifier of the field. For values, + Contains the type identifier of the field. For values, see enum ECPGttype in ecpgtype.h. @@ -2779,7 +4004,7 @@ typedef struct sqlda_struct sqlda_t; sqllen - It contains the binary length of the field. E.g. 4 bytes for ECPGt_int. + Contains the binary length of the field. e.g. 4 bytes for ECPGt_int. @@ -2788,7 +4013,8 @@ typedef struct sqlda_struct sqlda_t; sqldata - (char *)sqldata points to the data. + Points to the data. The format of the data is described + in . @@ -2797,8 +4023,8 @@ typedef struct sqlda_struct sqlda_t; sqlind - (char *)sqlind points to the NULL indicator for data. - 0 means NOT NULL, -1 means NULL. + Points to the null indicator. 0 means not null, -1 means + null. @@ -2807,22 +4033,37 @@ typedef struct sqlda_struct sqlda_t; sqlname - struct sqlname sqlname contains the name of the field - in a structure: + The the name of the field. + + + + + + + + + struct sqlname structure + + + A struct sqlname structure holds a column name. It + is used as a member of the sqlvar_t structure. The + definition of the structure is: +#define NAMEDATALEN 64 + struct sqlname { short length; char data[NAMEDATALEN]; }; - + The meaning of the fields is: length - sqlname.length contains the length of the field name. + Contains the length of the field name. @@ -2830,28 +4071,3756 @@ struct sqlname data - sqlname.data contains the actual field name. + Contains the actual field name. - - - + + + - + + Retreiving a result set using an SQLDA + + + + The general steps to retrieve a query result set through an + SQLDA are: + + Declare an sqlda_t structure to receive the result set. + Execute FETCH/EXECUTE/DESCRIBE commands to process a query specifying the declared SQLDA. + Check the number of records in the result set by looking at sqln, a member of the sqlda_t structure. + Get the values of each column from sqlvar[0], sqlvar[1], etc., members of the sqlda_t structure. + Go to next row (sqlda_t structure) by following the desc_next pointer, a member of the sqlda_t structure. + Repeat above as you need. + + + + Here is an example retrieving a result set through an SQLDA. + + + + First, declare a sqlda_t structure to receive the result set. + +sqlda_t *sqlda1; + + + + + Next, specify the SQLDA in a command. This is + a FETCH command example. + +EXEC SQL FETCH NEXT FROM cur1 INTO DESCRIPTOR sqlda1; + + + + + Run a loop following the linked list to retrieve the rows. + +sqlda_t *cur_sqlda; + +for (cur_sqlda = sqlda1; + cur_sqlda != NULL; + cur_sqlda = cur_sqlda->desc_next) +{ + ... +} + + + + + Inside the loop, run another loop to retrieve each column data + (sqlvar_t structure) of the row. + +for (i = 0; i < cur_sqlda->sqld; i++) +{ + sqlvar_t v = cur_sqlda->sqlvar[i]; + char *sqldata = v.sqldata; + short sqllen = v.sqllen; + ... +} + + + + + To get a column value, check the sqltype value, + a member of the sqlvar_t structure. Then, switch + to an appropriate way, depending on the column type, to copy + data from the sqlvar field to a host variable. + +char var_buf[1024]; + +switch (v.sqltype) +{ + case ECPGt_char: + memset(&var_buf, 0, sizeof(var_buf)); + memcpy(&var_buf, sqldata, (sizeof(var_buf) <= sqllen ? sizeof(var_buf) - 1 : sqllen)); + break; + + case ECPGt_int: /* integer */ + memcpy(&intval, sqldata, sqllen); + snprintf(var_buf, sizeof(var_buf), "%d", intval); + break; + + ... +} + + + + + + Passing query parameters using an SQLDA + + + + The general steps to use an SQLDA to pass input + parameters to a prepared query are: + + Create a prepared query (prepared statement) + Declare a sqlda_t structure as an input SQLDA. + Allocate memory area (as sqlda_t structure) for the input SQLDA. + Set (copy) input values in the allocated memory. + Open a cursor with specifying the input SQLDA. + + + + Here is an example. + + + + First, create a prepared statement. + +EXEC SQL BEGIN DECLARE SECTION; +char query[1024] = "SELECT d.oid, * FROM pg_database d, pg_stat_database s WHERE d.oid = s.datid AND (d.datname = ? OR d.oid = ?)"; +EXEC SQL END DECLARE SECTION; + +EXEC SQL PREPARE stmt1 FROM :query; + + + + + Next, allocate memory for an SQLDA, and set the number of input + parameters in sqln, a member variable of + the sqlda_t structure. When two or more input + parameters are required for the prepared query, the application + has to allocate additional memory space which is calculated by + (nr. of params - 1) * sizeof(sqlvar_t). The example shown here + allocates memory space for two input parameters. + +sqlda_t *sqlda2; + +sqlda2 = (sqlda_t *) malloc(sizeof(sqlda_t) + sizeof(sqlvar_t)); +memset(sqlda2, 0, sizeof(sqlda_t) + sizeof(sqlvar_t)); + +sqlda2->sqln = 2; /* number of input variables */ + + + + + After memory allocation, store the parameter values into the + sqlvar[] array. (This is same array used for + retrieving column values when the SQLDA is receiving a result + set.) In this example, the input parameters + are "postgres", having a string type, + and 1, having an integer type. + +sqlda2->sqlvar[0].sqltype = ECPGt_char; +sqlda2->sqlvar[0].sqldata = "postgres"; +sqlda2->sqlvar[0].sqllen = 8; + +int intval = 1; +sqlda2->sqlvar[1].sqltype = ECPGt_int; +sqlda2->sqlvar[1].sqldata = (char *) &intval; +sqlda2->sqlvar[1].sqllen = sizeof(intval); + + + + + By opening a cursor and specifying the SQLDA that was set up + beforehand, the input parameters are passed to the prepared + statement. + +EXEC SQL OPEN cur1 USING DESCRIPTOR sqlda2; + + + + + Finally, after using input SQLDAs, the allocated memory space + must be freed explicitly, unlike SQLDAs used for receiving query + results. + +free(sqlda2); + + + + + + A sample application using SQLDA + + + Here is an example program, which describes how to fetch access + statistics of the databases, specified by the input parameters, + from the system catalogs. + + + + This application joins two system tables, pg_database and + pg_stat_database on the database oid, and also fetches and shows + the database statistics which are retreived by two input + parameters (a database "postgres", and oid "1"). + + + + First, declare an SQLDA for input and an SQLDA for output. + +EXEC SQL include sqlda.h; + +sqlda_t *sqlda1; /* an output descriptor */ +sqlda_t *sqlda2; /* an input descriptor */ + + + + + Next, connect to the database, prepare a statement, and declare a + cursor for the prepared statement. + +int +main(void) +{ + EXEC SQL BEGIN DECLARE SECTION; + char query[1024] = "SELECT d.oid,* FROM pg_database d, pg_stat_database s WHERE d.oid=s.datid AND ( d.datname=? OR d.oid=? )"; + EXEC SQL END DECLARE SECTION; + + EXEC SQL CONNECT TO testdb AS con1 USER testuser; + + EXEC SQL PREPARE stmt1 FROM :query; + EXEC SQL DECLARE cur1 CURSOR FOR stmt1; + + + + + Next, put some values in the input SQLDA for the input + parameters. Allocate memory for the input SQLDA, and set the + number of input parameters to sqln. Store + type, value, and value length into sqltype, + sqldata, and sqllen in the + sqlvar structure. + + + /* Create SQLDA structure for input parameters. */ + sqlda2 = (sqlda_t *) malloc(sizeof(sqlda_t) + sizeof(sqlvar_t)); + memset(sqlda2, 0, sizeof(sqlda_t) + sizeof(sqlvar_t)); + sqlda2->sqln = 2; /* number of input variables */ + + sqlda2->sqlvar[0].sqltype = ECPGt_char; + sqlda2->sqlvar[0].sqldata = "postgres"; + sqlda2->sqlvar[0].sqllen = 8; + + intval = 1; + sqlda2->sqlvar[1].sqltype = ECPGt_int; + sqlda2->sqlvar[1].sqldata = (char *)&intval; + sqlda2->sqlvar[1].sqllen = sizeof(intval); + + + + + After setting up the input SQLDA, open a cursor with the input + SQLDA. + + + /* Open a cursor with input parameters. */ + EXEC SQL OPEN cur1 USING DESCRIPTOR sqlda2; + + + + + Fetch rows into the output SQLDA from the opened cursor. + (Generally, you have to call FETCH repeatedly + in the loop, to fetch all rows in the result set.) + + while (1) + { + sqlda_t *cur_sqlda; + + /* Assign descriptor to the cursor */ + EXEC SQL FETCH NEXT FROM cur1 INTO DESCRIPTOR sqlda1; + + + + + Next, retrieve the fetched records from the SQLDA, by following + the linked list of the sqlda_t structure. + + for (cur_sqlda = sqlda1 ; + cur_sqlda != NULL ; + cur_sqlda = cur_sqlda->desc_next) + { + ... + + + + + Read each columns in the first record. The number of columns is + stored in sqld, the actual data of the first + column is stored in sqlvar[0], both members of + the sqlda_t structure. + + + /* Print every column in a row. */ + for (i = 0; i < sqlda1->sqld; i++) + { + sqlvar_t v = sqlda1->sqlvar[i]; + char *sqldata = v.sqldata; + short sqllen = v.sqllen; + + strncpy(name_buf, v.sqlname.data, v.sqlname.length); + name_buf[v.sqlname.length] = '\0'; + + + + + Now, the column data is stored in the variable v. + Copy every datum into host variables, looking + at v.sqltype for the type of the column. + + switch (v.sqltype) { + int intval; + double doubleval; + unsigned long long int longlongval; + + case ECPGt_char: + memset(&var_buf, 0, sizeof(var_buf)); + memcpy(&var_buf, sqldata, (sizeof(var_buf) <= sqllen ? sizeof(var_buf)-1 : sqllen)); + break; + + case ECPGt_int: /* integer */ + memcpy(&intval, sqldata, sqllen); + snprintf(var_buf, sizeof(var_buf), "%d", intval); + break; + + ... + + default: + ... + } + + printf("%s = %s (type: %d)\n", name_buf, var_buf, v.sqltype); + } + + + + + Close the cursor after processing all of records, and disconnect + from the database. + + EXEC SQL CLOSE cur1; + EXEC SQL COMMIT; + + EXEC SQL DISCONNECT ALL; + + + + + The whole program is shown + in . + + + + Example SQLDA program + +#include <stdlib.h> +#include <string.h> +#include <stdlib.h> +#include <stdio.h> +#include <unistd.h> + +EXEC SQL include sqlda.h; + +sqlda_t *sqlda1; /* descriptor for output */ +sqlda_t *sqlda2; /* descriptor for input */ + +EXEC SQL WHENEVER NOT FOUND DO BREAK; +EXEC SQL WHENEVER SQLERROR STOP; + +int +main(void) +{ + EXEC SQL BEGIN DECLARE SECTION; + char query[1024] = "SELECT d.oid,* FROM pg_database d, pg_stat_database s WHERE d.oid=s.datid AND ( d.datname=? OR d.oid=? )"; + + int intval; + unsigned long long int longlongval; + EXEC SQL END DECLARE SECTION; + + EXEC SQL CONNECT TO uptimedb AS con1 USER uptime; + + EXEC SQL PREPARE stmt1 FROM :query; + EXEC SQL DECLARE cur1 CURSOR FOR stmt1; + + /* Create a SQLDA structure for an input parameter */ + sqlda2 = (sqlda_t *)malloc(sizeof(sqlda_t) + sizeof(sqlvar_t)); + memset(sqlda2, 0, sizeof(sqlda_t) + sizeof(sqlvar_t)); + sqlda2->sqln = 2; /* a number of input variables */ + + sqlda2->sqlvar[0].sqltype = ECPGt_char; + sqlda2->sqlvar[0].sqldata = "postgres"; + sqlda2->sqlvar[0].sqllen = 8; + + intval = 1; + sqlda2->sqlvar[1].sqltype = ECPGt_int; + sqlda2->sqlvar[1].sqldata = (char *) &intval; + sqlda2->sqlvar[1].sqllen = sizeof(intval); + + /* Open a cursor with input parameters. */ + EXEC SQL OPEN cur1 USING DESCRIPTOR sqlda2; + + while (1) + { + sqlda_t *cur_sqlda; + + /* Assign descriptor to the cursor */ + EXEC SQL FETCH NEXT FROM cur1 INTO DESCRIPTOR sqlda1; + + for (cur_sqlda = sqlda1 ; + cur_sqlda != NULL ; + cur_sqlda = cur_sqlda->desc_next) + { + int i; + char name_buf[1024]; + char var_buf[1024]; + + /* Print every column in a row. */ + for (i=0 ; i<cur_sqlda->sqld ; i++) + { + sqlvar_t v = cur_sqlda->sqlvar[i]; + char *sqldata = v.sqldata; + short sqllen = v.sqllen; + + strncpy(name_buf, v.sqlname.data, v.sqlname.length); + name_buf[v.sqlname.length] = '\0'; + + switch (v.sqltype) + { + case ECPGt_char: + memset(&var_buf, 0, sizeof(var_buf)); + memcpy(&var_buf, sqldata, (sizeof(var_buf)<=sqllen ? sizeof(var_buf)-1 : sqllen) ); + break; + + case ECPGt_int: /* integer */ + memcpy(&intval, sqldata, sqllen); + snprintf(var_buf, sizeof(var_buf), "%d", intval); + break; + + case ECPGt_long_long: /* bigint */ + memcpy(&longlongval, sqldata, sqllen); + snprintf(var_buf, sizeof(var_buf), "%lld", longlongval); + break; + + default: + { + int i; + memset(var_buf, 0, sizeof(var_buf)); + for (i = 0; i < sqllen; i++) + { + char tmpbuf[16]; + snprintf(tmpbuf, sizeof(tmpbuf), "%02x ", (unsigned char) sqldata[i]); + strncat(var_buf, tmpbuf, sizeof(var_buf)); + } + } + break; + } + + printf("%s = %s (type: %d)\n", name_buf, var_buf, v.sqltype); + } + + printf("\n"); + } + } + + EXEC SQL CLOSE cur1; + EXEC SQL COMMIT; + + EXEC SQL DISCONNECT ALL; + + return 0; +} + + + + The output of this example should look something like the + following (some numbers will vary). + + + +oid = 1 (type: 1) +datname = template1 (type: 1) +datdba = 10 (type: 1) +encoding = 0 (type: 5) +datistemplate = t (type: 1) +datallowconn = t (type: 1) +datconnlimit = -1 (type: 5) +datlastsysoid = 11510 (type: 1) +datfrozenxid = 379 (type: 1) +dattablespace = 1663 (type: 1) +datconfig = (type: 1) +datacl = {=c/uptime,uptime=CTc/uptime} (type: 1) +datid = 1 (type: 1) +datname = template1 (type: 1) +numbackends = 0 (type: 5) +xact_commit = 113606 (type: 9) +xact_rollback = 0 (type: 9) +blks_read = 130 (type: 9) +blks_hit = 7341714 (type: 9) +tup_returned = 38262679 (type: 9) +tup_fetched = 1836281 (type: 9) +tup_inserted = 0 (type: 9) +tup_updated = 0 (type: 9) +tup_deleted = 0 (type: 9) + +oid = 11511 (type: 1) +datname = postgres (type: 1) +datdba = 10 (type: 1) +encoding = 0 (type: 5) +datistemplate = f (type: 1) +datallowconn = t (type: 1) +datconnlimit = -1 (type: 5) +datlastsysoid = 11510 (type: 1) +datfrozenxid = 379 (type: 1) +dattablespace = 1663 (type: 1) +datconfig = (type: 1) +datacl = (type: 1) +datid = 11511 (type: 1) +datname = postgres (type: 1) +numbackends = 0 (type: 5) +xact_commit = 221069 (type: 9) +xact_rollback = 18 (type: 9) +blks_read = 1176 (type: 9) +blks_hit = 13943750 (type: 9) +tup_returned = 77410091 (type: 9) +tup_fetched = 3253694 (type: 9) +tup_inserted = 0 (type: 9) +tup_updated = 0 (type: 9) +tup_deleted = 0 (type: 9) + + + + + + + + Error Handling + + + This section describes how you can handle exceptional conditions + and warnings in an embedded SQL program. There are two + nonexclusive facilities for this. + + + + + Callbacks can be configured to handle warning and error + conditions using the WHENEVER command. + + + + + + Detailed information about the error or warning can be obtained + from the sqlca variable. + + + + + + + Setting callbacks + + + One simple method to catch errors and warnings is to set a + specific action to be executed whenever a particular condition + occurs. In general: + +EXEC SQL WHENEVER condition action; + + + + + condition can be one of the following: + + + + SQLERROR + + + The specified action is called whenever an error occurs during + the execution of an SQL statement. + + + + + + SQLWARNING + + + The specified action is called whenever a warning occurs + during the execution of an SQL statement. + + + + + + NOT FOUND + + + The specified action is called whenever an SQL statement + retrieves or affects zero rows. (This condition is not an + error, but you might be interested in handling it specially.) + + action can be one of the following: + + + + CONTINUE + + + This effectively means that the condition is ignored. This is + the default. + + + + + + GOTO label + GO TO label + + + Jump to the specified label (using a C goto + statement). + + + + + + SQLPRINT + + + Print a message to standard error. This is useful for simple + programs or during prototyping. The details of the message + cannot be configured. + + + + + + STOP + + + Call exit(1), which will terminate the + program. + + + + + + DO BREAK + + + Execute the C statement break. This should + only be used in loops or switch statements. + + + + + + CALL name (args) + DO name (args) + + + Call the specified C functions with the specified arguments. + + + + + + The SQL standard only provides for the actions + CONTINUE and GOTO (and + GO TO). + + + + Here is an example that you might want to use in a simple program. + It prints a simple message when a warning occurs and aborts the + program when an error happens: + +EXEC SQL WHENEVER SQLWARNING SQLPRINT; +EXEC SQL WHENEVER SQLERROR STOP; + + + + + The statement EXEC SQL WHENEVER is a directive + of the SQL preprocessor, not a C statement. The error or warning + actions that it sets apply to all embedded SQL statements that + appear below the point where the handler is set, unless a + different action was set for the same condition between the first + EXEC SQL WHENEVER and the SQL statement causing + the condition, regardless of the flow of control in the C program. + So neither of the two following C program excerpts will have the + desired effect: + +/* + * WRONG + */ +int main(int argc, char *argv[]) +{ + ... + if (verbose) { + EXEC SQL WHENEVER SQLWARNING SQLPRINT; + } + ... + EXEC SQL SELECT ...; + ... +} + + + +/* + * WRONG + */ +int main(int argc, char *argv[]) +{ + ... + set_error_handler(); + ... + EXEC SQL SELECT ...; + ... +} + +static void set_error_handler(void) +{ + EXEC SQL WHENEVER SQLERROR STOP; +} + + + + sqlca + + + For more powerful error handling, the embedded SQL interface + provides a global variable with the name sqlca + (SQL communication area) + that has the following structure: + +struct +{ + char sqlcaid[8]; + long sqlabc; + long sqlcode; + struct + { + int sqlerrml; + char sqlerrmc[SQLERRMC_LEN]; + } sqlerrm; + char sqlerrp[8]; + long sqlerrd[6]; + char sqlwarn[8]; + char sqlstate[5]; +} sqlca; + + (In a multithreaded program, every thread automatically gets its + own copy of sqlca. This works similarly to the + handling of the standard C global variable + errno.) + + + + sqlca covers both warnings and errors. If + multiple warnings or errors occur during the execution of a + statement, then sqlca will only contain + information about the last one. + + + + If no error occurred in the last SQL statement, + sqlca.sqlcode will be 0 and + sqlca.sqlstate will be + "00000". If a warning or error occurred, then + sqlca.sqlcode will be negative and + sqlca.sqlstate will be different from + "00000". A positive + sqlca.sqlcode indicates a harmless condition, + such as that the last query returned zero rows. + sqlcode and sqlstate are two + different error code schemes; details appear below. + + + + If the last SQL statement was successful, then + sqlca.sqlerrd[1] contains the OID of the + processed row, if applicable, and + sqlca.sqlerrd[2] contains the number of + processed or returned rows, if applicable to the command. + + + + In case of an error or warning, + sqlca.sqlerrm.sqlerrmc will contain a string + that describes the error. The field + sqlca.sqlerrm.sqlerrml contains the length of + the error message that is stored in + sqlca.sqlerrm.sqlerrmc (the result of + strlen(), not really interesting for a C + programmer). Note that some messages are too long to fit in the + fixed-size sqlerrmc array; they will be truncated. + + + + In case of a warning, sqlca.sqlwarn[2] is set + to W. (In all other cases, it is set to + something different from W.) If + sqlca.sqlwarn[1] is set to + W, then a value was truncated when it was + stored in a host variable. sqlca.sqlwarn[0] is + set to W if any of the other elements are set + to indicate a warning. + + + + The fields sqlcaid, + sqlcabc, + sqlerrp, and the remaining elements of + sqlerrd and + sqlwarn currently contain no useful + information. + + + + The structure sqlca is not defined in the SQL + standard, but is implemented in several other SQL database + systems. The definitions are similar at the core, but if you want + to write portable applications, then you should investigate the + different implementations carefully. + + + + Here is one example that combines the use of WHENEVER + and sqlca, printing out the contents + of sqlca when an error occurs. This is perhaps + useful for debugging or prototyping applications, before + installing a more user-friendly error handler. + + +EXEC SQL WHENEVER SQLERROR CALL print_sqlca(); + +void +print_sqlca() +{ + fprintf(stderr, "==== sqlca ====\n"); + fprintf(stderr, "sqlcode: %ld\n", sqlca.sqlcode); + fprintf(stderr, "sqlerrm.sqlerrml: %d\n", sqlca.sqlerrm.sqlerrml); + fprintf(stderr, "sqlerrm.sqlerrmc: %s\n", sqlca.sqlerrm.sqlerrmc); + fprintf(stderr, "sqlerrd: %ld %ld %ld %ld %ld %ld\n", sqlca.sqlerrd[0],sqlca.sqlerrd[1],sqlca.sqlerrd[2], + sqlca.sqlerrd[3],sqlca.sqlerrd[4],sqlca.sqlerrd[5]); + fprintf(stderr, "sqlwarn: %d %d %d %d %d %d %d %d\n", sqlca.sqlwarn[0], sqlca.sqlwarn[1], sqlca.sqlwarn[2], + sqlca.sqlwarn[3], sqlca.sqlwarn[4], sqlca.sqlwarn[5], + sqlca.sqlwarn[6], sqlca.sqlwarn[7]); + fprintf(stderr, "sqlstate: %5s\n", sqlca.sqlstate); + fprintf(stderr, "===============\n"); +} + + + The result could look as follows (here an error due to a + misspelled table name): + + +==== sqlca ==== +sqlcode: -400 +sqlerrm.sqlerrml: 49 +sqlerrm.sqlerrmc: relation "pg_databasep" does not exist on line 38 +sqlerrd: 0 0 0 0 0 0 +sqlwarn: 0 0 0 0 0 0 0 0 +sqlstate: 42P01 +=============== + + + + + + <literal>SQLSTATE</literal> vs <literal>SQLCODE</literal> + + + The fields sqlca.sqlstate and + sqlca.sqlcode are two different schemes that + provide error codes. Both are derived from the SQL standard, but + SQLCODE has been marked deprecated in the SQL-92 + edition of the standard and has been dropped in later editions. + Therefore, new applications are strongly encouraged to use + SQLSTATE. + + + + SQLSTATE is a five-character array. The five + characters contain digits or upper-case letters that represent + codes of various error and warning conditions. + SQLSTATE has a hierarchical scheme: the first + two characters indicate the general class of the condition, the + last three characters indicate a subclass of the general + condition. A successful state is indicated by the code + 00000. The SQLSTATE codes are for + the most part defined in the SQL standard. The + PostgreSQL server natively supports + SQLSTATE error codes; therefore a high degree + of consistency can be achieved by using this error code scheme + throughout all applications. For further information see + . + + + + SQLCODE, the deprecated error code scheme, is a + simple integer. A value of 0 indicates success, a positive value + indicates success with additional information, a negative value + indicates an error. The SQL standard only defines the positive + value +100, which indicates that the last command returned or + affected zero rows, and no specific negative values. Therefore, + this scheme can only achieve poor portability and does not have a + hierarchical code assignment. Historically, the embedded SQL + processor for PostgreSQL has assigned + some specific SQLCODE values for its use, which + are listed below with their numeric value and their symbolic name. + Remember that these are not portable to other SQL implementations. + To simplify the porting of applications to the + SQLSTATE scheme, the corresponding + SQLSTATE is also listed. There is, however, no + one-to-one or one-to-many mapping between the two schemes (indeed + it is many-to-many), so you should consult the global + SQLSTATE listing in + in each case. + + + + These are the assigned SQLCODE values: + + + + 0 (ECPG_NO_ERROR) + + + Indicates no error. (SQLSTATE 00000) + + + + + + 100 (ECPG_NOT_FOUND) + + + This is a harmless condition indicating that the last command + retrieved or processed zero rows, or that you are at the end of + the cursor. (SQLSTATE 02000) + + + + When processing a cursor in a loop, you could use this code as + a way to detect when to abort the loop, like this: + +while (1) +{ + EXEC SQL FETCH ... ; + if (sqlca.sqlcode == ECPG_NOT_FOUND) + break; +} + + But WHENEVER NOT FOUND DO BREAK effectively + does this internally, so there is usually no advantage in + writing this out explicitly. + + + + + + -12 (ECPG_OUT_OF_MEMORY) + + + Indicates that your virtual memory is exhausted. The numeric + value is defined as -ENOMEM. (SQLSTATE + YE001) + + + + + + -200 (ECPG_UNSUPPORTED) + + + Indicates the preprocessor has generated something that the + library does not know about. Perhaps you are running + incompatible versions of the preprocessor and the + library. (SQLSTATE YE002) + + + + + + -201 (ECPG_TOO_MANY_ARGUMENTS) + + + This means that the command specified more host variables than + the command expected. (SQLSTATE 07001 or 07002) + + + + + + -202 (ECPG_TOO_FEW_ARGUMENTS) + + + This means that the command specified fewer host variables than + the command expected. (SQLSTATE 07001 or 07002) + + + + + + -203 (ECPG_TOO_MANY_MATCHES) + + + This means a query has returned multiple rows but the statement + was only prepared to store one result row (for example, because + the specified variables are not arrays). (SQLSTATE 21000) + + + + + + -204 (ECPG_INT_FORMAT) + + + The host variable is of type int and the datum in + the database is of a different type and contains a value that + cannot be interpreted as an int. The library uses + strtol() for this conversion. (SQLSTATE + 42804) + + + + + + -205 (ECPG_UINT_FORMAT) + + + The host variable is of type unsigned int and the + datum in the database is of a different type and contains a + value that cannot be interpreted as an unsigned + int. The library uses strtoul() + for this conversion. (SQLSTATE 42804) + + + + + + -206 (ECPG_FLOAT_FORMAT) + + + The host variable is of type float and the datum + in the database is of another type and contains a value that + cannot be interpreted as a float. The library + uses strtod() for this conversion. + (SQLSTATE 42804) + + + + + + -207 (ECPG_NUMERIC_FORMAT) + + + The host variable is of type numeric and the datum + in the database is of another type and contains a value that + cannot be interpreted as a numeric value. + (SQLSTATE 42804) + + + + + + -208 (ECPG_INTERVAL_FORMAT) + + + The host variable is of type interval and the datum + in the database is of another type and contains a value that + cannot be interpreted as an interval value. + (SQLSTATE 42804) + + + + + + -209 (ECPG_DATE_FORMAT) + + + The host variable is of type date and the datum in + the database is of another type and contains a value that + cannot be interpreted as a date value. + (SQLSTATE 42804) + + + + + + -210 (ECPG_TIMESTAMP_FORMAT) + + + The host variable is of type timestamp and the + datum in the database is of another type and contains a value + that cannot be interpreted as a timestamp value. + (SQLSTATE 42804) + + + + + + -211 (ECPG_CONVERT_BOOL) + + + This means the host variable is of type bool and + the datum in the database is neither 't' nor + 'f'. (SQLSTATE 42804) + + + + + + -212 (ECPG_EMPTY) + + + The statement sent to the PostgreSQL + server was empty. (This cannot normally happen in an embedded + SQL program, so it might point to an internal error.) (SQLSTATE + YE002) + + + + + + -213 (ECPG_MISSING_INDICATOR) + + + A null value was returned and no null indicator variable was + supplied. (SQLSTATE 22002) + + + + + + -214 (ECPG_NO_ARRAY) + + + An ordinary variable was used in a place that requires an + array. (SQLSTATE 42804) + + + + + + -215 (ECPG_DATA_NOT_ARRAY) + + + The database returned an ordinary variable in a place that + requires array value. (SQLSTATE 42804) + + + + + + + -216 (ECPG_ARRAY_INSERT) + + + The value could not be inserted into the array. (SQLSTATE + 42804) + + + +]]> + + + -220 (ECPG_NO_CONN) + + + The program tried to access a connection that does not exist. + (SQLSTATE 08003) + + + + + + -221 (ECPG_NOT_CONN) + + + The program tried to access a connection that does exist but is + not open. (This is an internal error.) (SQLSTATE YE002) + + + + + + -230 (ECPG_INVALID_STMT) + + + The statement you are trying to use has not been prepared. + (SQLSTATE 26000) + + + + + + -239 (ECPG_INFORMIX_DUPLICATE_KEY) + + + Duplicate key error, violation of unique constraint (Informix + compatibility mode). (SQLSTATE 23505) + + + + + + -240 (ECPG_UNKNOWN_DESCRIPTOR) + + + The descriptor specified was not found. The statement you are + trying to use has not been prepared. (SQLSTATE 33000) + + + + + + -241 (ECPG_INVALID_DESCRIPTOR_INDEX) + + + The descriptor index specified was out of range. (SQLSTATE + 07009) + + + + + + -242 (ECPG_UNKNOWN_DESCRIPTOR_ITEM) + + + An invalid descriptor item was requested. (This is an internal + error.) (SQLSTATE YE002) + + + + + + -243 (ECPG_VAR_NOT_NUMERIC) + + + During the execution of a dynamic statement, the database + returned a numeric value and the host variable was not numeric. + (SQLSTATE 07006) + + + + + + -244 (ECPG_VAR_NOT_CHAR) + + + During the execution of a dynamic statement, the database + returned a non-numeric value and the host variable was numeric. + (SQLSTATE 07006) + + + + + + -284 (ECPG_INFORMIX_SUBSELECT_NOT_ONE) + + + A result of the subquery is not single row (Informix + compatibility mode). (SQLSTATE 21000) + + + + + + -400 (ECPG_PGSQL) + + + Some error caused by the PostgreSQL + server. The message contains the error message from the + PostgreSQL server. + + + + + + -401 (ECPG_TRANS) + + + The PostgreSQL server signaled that + we cannot start, commit, or rollback the transaction. + (SQLSTATE 08007) + + + + + + -402 (ECPG_CONNECT) + + + The connection attempt to the database did not succeed. + (SQLSTATE 08001) + + + + + + -403 (ECPG_DUPLICATE_KEY) + + + Duplicate key error, violation of unique constraint. (SQLSTATE + 23505) + + + + + + -404 (ECPG_SUBSELECT_NOT_ONE) + + + A result for the subquery is not single row. (SQLSTATE 21000) + + + + + + + -600 (ECPG_WARNING_UNRECOGNIZED) + + + An unrecognized warning was received from the server. + + + + + + -601 (ECPG_WARNING_QUERY_IGNORED) + + + Current transaction is aborted. Queries are ignored until the + end of the transaction block. + + + +]]> + + + -602 (ECPG_WARNING_UNKNOWN_PORTAL) + + + An invalid cursor name was specified. (SQLSTATE 34000) + + + + + + -603 (ECPG_WARNING_IN_TRANSACTION) + + + Transaction is in progress. (SQLSTATE 25001) + + + + + + -604 (ECPG_WARNING_NO_TRANSACTION) + + + There is no active (in-progress) transaction. (SQLSTATE 25P01) + + + + + + -605 (ECPG_WARNING_PORTAL_EXISTS) + + + An existing cursor name was specified. (SQLSTATE 42P03) + + + + + + + + + + + Preprocessor directives + + + Several preprocessor directives are available that modify how + the ecpg preprocessor parses and processes a + file. + + + + Including files + + + To include an external file into your embedded SQL program, use: + +EXEC SQL INCLUDE filename; +EXEC SQL INCLUDE <filename>; +EXEC SQL INCLUDE "filename"; + + The embedded SQL preprocessor will look for a file named + filename.h, + preprocess it, and include it in the resulting C output. Thus, + embedded SQL statements in the included file are handled correctly. + + + + The ecpg preprocessor will search a file at + several directories in following order: + + + current directory + /usr/local/include + PostgreSQL include directory, defined at build time (e.g., /usr/local/pgsql/include) + /usr/include + + + But when EXEC SQL INCLUDE + "filename" is used, only the + current directory is searched. + + + + In each directory, the preprocessor will first look for the file + name as given, and if not found will append .h + to the file name and try again (unless the specified file name + already has that suffix). + + + + Note that EXEC SQL INCLUDE is not the same as: + +#include <filename.h> + + because this file would not be subject to SQL command preprocessing. + Naturally, you can continue to use the C + #include directive to include other header + files. + + + + + The include file name is case-sensitive, even though the rest of + the EXEC SQL INCLUDE command follows the normal + SQL case-sensitivity rules. + + + + + + The define and undef directives + + Similar to the directive #define that is known from C, + embedded SQL has a similar concept: + +EXEC SQL DEFINE name; +EXEC SQL DEFINE name value; + + So you can define a name: + +EXEC SQL DEFINE HAVE_FEATURE; + + And you can also define constants: + +EXEC SQL DEFINE MYNUMBER 12; +EXEC SQL DEFINE MYSTRING 'abc'; + + Use undef to remove a previous definition: + +EXEC SQL UNDEF MYNUMBER; + + + + + Of course you can continue to use the C versions #define + and #undef in your embedded SQL program. The difference + is where your defined values get evaluated. If you use EXEC SQL + DEFINE then the ecpg preprocessor evaluates the defines and substitutes + the values. For example if you write: + +EXEC SQL DEFINE MYNUMBER 12; +... +EXEC SQL UPDATE Tbl SET col = MYNUMBER; + + then ecpg will already do the substitution and your C compiler will never + see any name or identifier MYNUMBER. Note that you cannot use + #define for a constant that you are going to use in an + embedded SQL query because in this case the embedded SQL precompiler is not + able to see this declaration. + + + + + ifdef, ifndef, else, elif, and endif directives + + You can use the following directives to compile code sections conditionally: + + + + EXEC SQL ifdef name; + + + Checks a name and processes subsequent lines if + name has been created with EXEC SQL define + name. + + + + + + EXEC SQL ifndef name; + + + Checks a name and processes subsequent lines if + name has not been created with + EXEC SQL define name. + + + + + + EXEC SQL else; + + + Starts processing an alternative section to a section introduced by + either EXEC SQL ifdef name or + EXEC SQL ifndef name. + + + + + + EXEC SQL elif name; + + + Checks name and starts an alternative section if + name has been created with EXEC SQL define + name. + + + + + + EXEC SQL endif; + + + Ends an alternative section. + + + + + + + + Example: + +EXEC SQL ifndef TZVAR; +EXEC SQL SET TIMEZONE TO 'GMT'; +EXEC SQL elif TZNAME; +EXEC SQL SET TIMEZONE TO TZNAME; +EXEC SQL else; +EXEC SQL SET TIMEZONE TO TZVAR; +EXEC SQL endif; + + + + + + + + Processing Embedded SQL Programs + + + Now that you have an idea how to form embedded SQL C programs, you + probably want to know how to compile them. Before compiling you + run the file through the embedded SQL + C preprocessor, which converts the + SQL statements you used to special function + calls. After compiling, you must link with a special library that + contains the needed functions. These functions fetch information + from the arguments, perform the SQL command using + the libpq interface, and put the result + in the arguments specified for output. + + + + The preprocessor program is called ecpg and is + included in a normal PostgreSQL installation. + Embedded SQL programs are typically named with an extension + .pgc. If you have a program file called + prog1.pgc, you can preprocess it by simply + calling: + +ecpg prog1.pgc + + This will create a file called prog1.c. If + your input files do not follow the suggested naming pattern, you + can specify the output file explicitly using the + option. + + + + The preprocessed file can be compiled normally, for example: + +cc -c prog1.c + + The generated C source files include header files from the + PostgreSQL installation, so if you installed + PostgreSQL in a location that is not searched by + default, you have to add an option such as + -I/usr/local/pgsql/include to the compilation + command line. + + + + To link an embedded SQL program, you need to include the + libecpg library, like so: + +cc -o myprog prog1.o prog2.o ... -lecpg + + Again, you might have to add an option like + -L/usr/local/pgsql/lib to that command line. + + + + If you manage the build process of a larger project using + make, it might be convenient to include + the following implicit rule to your makefiles: + +ECPG = ecpg + +%.c: %.pgc + $(ECPG) $< + + + + + The complete syntax of the ecpg command is + detailed in . + + + + The ecpg library is thread-safe by + default. However, you might need to use some threading + command-line options to compile your client code. + + + + + Library Functions + + + The libecpg library primarily contains + hidden functions that are used to implement the + functionality expressed by the embedded SQL commands. But there + are some functions that can usefully be called directly. Note that + this makes your code unportable. + + + + + + ECPGdebug(int on, FILE + *stream) turns on debug + logging if called with the first argument non-zero. Debug logging + is done on stream. The log contains + all SQL statements with all the input + variables inserted, and the results from the + PostgreSQL server. This can be very + useful when searching for errors in your SQL + statements. + + + + On Windows, if the ecpg libraries and an application are + compiled with different flags, this function call will crash the + application because the internal representation of the + FILE pointers differ. Specifically, + multithreaded/single-threaded, release/debug, and static/dynamic + flags should be the same for the library and all applications using + that library. + + + + + + + ECPGget_PGconn(const char *connection_name) + returns the library database connection handle identified by the given name. + If connection_name is set to NULL, the current + connection handle is returned. If no connection handle can be identified, the function returns + NULL. The returned connection handle can be used to call any other functions + from libpq, if necessary. + + + + It is a bad idea to manipulate database connection handles made from ecpg directly + with libpq routines. + + + + + + + ECPGtransactionStatus(const char *connection_name) + returns the current transaction status of the given connection identified by connection_name. + See and libpq's PQtransactionStatus() for details about the returned status codes. + + + + + + ECPGstatus(int lineno, + const char* connection_name) + returns true if you are connected to a database and false if not. + connection_name can be NULL + if a single connection is being used. + + + + + + + Large Objects + + + Large objects are not directly supported by ECPG, but ECPG + application can manipulate large objects through the libpq large + object functions, obtaining the necessary PGconn + object by calling the ECPGget_PGconn() + function. (However, use of + the ECPGget_PGconn() function and touching + PGconn objects directly should be done very carefully + and ideally not mixed with other ECPG database access calls.) + + + + For more details about the ECPGget_PGconn(), see + . For information about the large + object function interface, see . + + + + Large object functions have to be called in a transaction block, so + when autocommit is off, BEGIN commands have to + be isssued explicitly. + + + + shows an example program that + illustrates how to create, write, and read a large object in an + ECPG application. + + + + ECPG program accessing large objects + +#include +#include +#include + +EXEC SQL WHENEVER SQLERROR STOP; + +int +main(void) +{ + PGconn *conn; + Oid loid; + int fd; + char buf[256]; + int buflen = 256; + char buf2[256]; + int rc; + + memset(buf, 1, buflen); + + EXEC SQL CONNECT TO testdb AS con1; + + conn = ECPGget_PGconn("con1"); + printf("conn = %p\n", conn); + + /* create */ + loid = lo_create(conn, 0); + if (loid < 0) + printf("lo_create() failed: %s", PQerrorMessage(conn)); + + printf("loid = %d\n", loid); + + /* write test */ + fd = lo_open(conn, loid, INV_READ|INV_WRITE); + if (fd < 0) + printf("lo_open() failed: %s", PQerrorMessage(conn)); + + printf("fd = %d\n", fd); + + rc = lo_write(conn, fd, buf, buflen); + if (rc < 0) + printf("lo_write() failed\n"); + + rc = lo_close(conn, fd); + if (rc < 0) + printf("lo_close() failed: %s", PQerrorMessage(conn)); + + /* read test */ + fd = lo_open(conn, loid, INV_READ); + if (fd < 0) + printf("lo_open() failed: %s", PQerrorMessage(conn)); + + printf("fd = %d\n", fd); + + rc = lo_read(conn, fd, buf2, buflen); + if (rc < 0) + printf("lo_read() failed\n"); + + rc = lo_close(conn, fd); + if (rc < 0) + printf("lo_close() failed: %s", PQerrorMessage(conn)); + + /* check */ + rc = memcmp(buf, buf2, buflen); + printf("memcmp() = %d\n", rc); + + /* cleanup */ + rc = lo_unlink(conn, loid); + if (rc < 0) + printf("lo_unlink() failed: %s", PQerrorMessage(conn)); + + EXEC SQL COMMIT; + EXEC SQL DISCONNECT ALL; + return 0; +} +]]> + + + + + <acronym>C++</acronym> Applications + + + ECPG has some limited support for C++ applications. This section + describes some caveats. + + + + The ecpg preprocessor takes an input file + written in C (or something like C) and embedded SQL commands, + converts the embedded SQL commands into C language chunks, and + finally generates a .c file. The header file + declarations of the library functions used by the C language chunks + that ecpg generates are wrapped + in extern "C" { ... } blocks when used under + C++, so they should work seamlessly in C++. + + + + In general, however, the ecpg preprocessor only + understands C; it does not handle the special syntax and reserved + words of the C++ language. So, some embedded SQL code written in + C++ application code that uses complicated features specific to C++ + might fail to be preprocessed correctly or might not work as + expected. + + + + A safe way to use the embedded SQL code in a C++ application is + hiding the ECPG calls in a C module, which the C++ application code + calls into to access the database, and linking that together with + the rest of the C++ code. See + about that. + + + + Scope for host variables + + + The ecpg preprocessor understands the scope of + variables in C. In the C language, this is rather simple because + the scopes of variables is based on their code blocks. In C++, + however, the class member variables are referenced in a different + code block from the declared position, so + the ecpg preprocessor will not understand the + scope of the class member variables. + + + + For example, in the following case, the ecpg + preprocessor cannot find any declaration for the + variable dbname in the test + method, so an error will occur. + + +class TestCpp +{ + EXEC SQL BEGIN DECLARE SECTION; + char dbname[1024]; + EXEC SQL END DECLARE SECTION; + + public: + TestCpp(); + void test(); + ~TestCpp(); +}; + +TestCpp::TestCpp() +{ + EXEC SQL CONNECT TO testdb1; +} + +void Test::test() +{ + EXEC SQL SELECT current_database() INTO :dbname; + printf("current_database = %s\n", dbname); +} + +TestCpp::~TestCpp() +{ + EXEC SQL DISCONNECT ALL; +} + + + This code will result in an error like this: + +ecpg test_cpp.pgc +test_cpp.pgc:28: ERROR: variable "dbname" is not declared + + + + + To avoid this scope issue, the test method + could be modified to use a local variable as intermediate storage. + But this approach is only a poor workaround, because it uglifies + the code and reduces performance. + + +void TestCpp::test() +{ + EXEC SQL BEGIN DECLARE SECTION; + char tmp[1024]; + EXEC SQL END DECLARE SECTION; + + EXEC SQL SELECT current_database() INTO :tmp; + strlcpy(dbname, tmp, sizeof(tmp)); + + printf("current_database = %s\n", dbname); +} + + + + + + C++ application development with external C module + + + If you understand these technical limitations of + the ecpg preprocessor in C++, you might come to + the conclusion that linking C objects and C++ objects at the link + stage to enable C++ applications to use ECPG features could be + better than writing some embedded SQL commands in C++ code + directly. This section describes a way to separate some embedded + SQL commands from C++ application code with a simple example. In + this example, the application is implemented in C++, while C and + ECPG is used to connect to the PostgreSQL server. + + + + Three kinds of files have to be created: a C file + (*.pgc), a header file, and a C++ file: + + + + test_mod.pgc + + + A sub-routine module to execute SQL commands embedded in C. + It is going to be converted + into test_mod.c by the preprocessor. + + +#include "test_mod.h" +#include <stdio.h> + +void +db_connect() +{ + EXEC SQL CONNECT TO testdb1; +} + +void +db_test() +{ + EXEC SQL BEGIN DECLARE SECTION; + char dbname[1024]; + EXEC SQL END DECLARE SECTION; + + EXEC SQL SELECT current_database() INTO :dbname; + printf("current_database = %s\n", dbname); +} + +void +db_disconnect() +{ + EXEC SQL DISCONNECT ALL; +} + + + + + + + test_mod.h + + + A header file with declarations of the functions in the C + module (test_mod.pgc). It is included by + test_cpp.cpp. This file has to have an + extern "C" block around the declarations, + because it will be linked from the C++ module. + + +#ifdef __cplusplus +extern "C" { +#endif + +void db_connect(); +void db_test(); +void db_disconnect(); + +#ifdef __cplusplus +} +#endif + + + + + + + test_cpp.cpp + + + The main code for the application, including + the main routine, and in this example a + C++ class. + + +#include "test_mod.h" + +class TestCpp +{ + public: + TestCpp(); + void test(); + ~TestCpp(); +}; + +TestCpp::TestCpp() +{ + db_connect(); +} + +void +TestCpp::test() +{ + db_test(); +} + +TestCpp::~TestCpp() +{ + db_disconnect(); +} + +int +main(void) +{ + TestCpp *t = new TestCpp(); + + t->test(); + return 0; +} + + + + + + + + + To build the application, proceed as follows. Convert + test_mod.pgc into test_mod.c by + running ecpg, and generate + test_mod.o by compiling + test_mod.c with the C compiler: + +ecpg -o test_mod.c test_mod.pgc +cc -c test_mod.c -o test_mod.o + + + + + Next, generate test_cpp.o by compiling + test_cpp.cpp with the C++ compiler:. + +c++ -c test_cpp.cpp -o test_cpp.o + + + + + Finally, link these object files, test_cpp.o + and test_mod.o, into one executable, using the C++ + compiler driver: + +c++ test_cpp.o test_mod.o -lecpg -o test_cpp + + + + + + + Embedded SQL Commands + + + This section describes all SQL commands that are specific to + embedded SQL. Also refer to the SQL commands listed + in , which can also be used in + embedded SQL, unless stated otherwise. + + + + + ALLOCATE DESCRIPTOR + allocate an SQL descriptor area + + + + +ALLOCATE DESCRIPTOR name + + + + + Description + + + ALLOCATE DESCRIPTOR allocates a new named SQL + descriptor area, which can be used to exchange data between the + PostgreSQL server and the host program. + + + + Descriptor areas should be freed after use using + the DEALLOCATE DESCRIPTOR command. + + + + + Parameters + + + + name + + + A name of SQL descriptor, case sensitive. This can be an SQL + identifier or a host variable. + + + + + + + + Examples + + +EXEC SQL ALLOCATE DESCRIPTOR mydesc; + + + + + Compatibility + + + ALLOCATE DESCRIPTOR is specified in the SQL + standard. + + + + + See Also + + + + + + + + + + + + CONNECT + establish a database connection + + + + +CONNECT TO connection_target [ AS connection_name ] [ USER connection_user_name ] +CONNECT TO DEFAULT +CONNECT connection_user_name +DATABASE connection_target + + + + + Description + + + The CONNECT command establishes a connection + between the client and the PostgreSQL server. + + + + + Parameters + + + + connection_target + + + connection_target + specifies the target server of the connection on one of + several forms. + + + + [ database_name ] [ @host ] [ :port ] + + + Connect over TCP/IP + + + + + + unix:postgresql://host [ :port ] / [ database_name ] [ ?connection_option ] + + + Connect over Unix-domain sockets + + + + + + tcp:postgresql://host [ :port ] / [ database_name ] [ ?connection_option ] + + + Connect over TCP/IP + + + + + + SQL string constant + + + containing a value in one of the above forms + + + + + + host variable + + + host variable of type char[] + or VARCHAR[] containing a value in one of the + above forms + + + + + + + + + + connection_object + + + An optional identifier for the connection, so that it can be + referred to in other commands. This can be an SQL identifier + or a host variable. + + + + + + connection_user + + + The user name for the database connection. + + + + This parameter can also specify user name and password, using one the forms + user_name/password, + user_name IDENTIFIED BY password, or + user_name USING password. + + + + User name and password can be SQL identifiers, string + constants, or host variables. + + + + + + DEFAULT + + + Use all default connection parameters, as defined by libpq. + + + + + + + + Examples + + + Here a several variants for specifying connection parameters: + +EXEC SQL CONNECT TO "connectdb" AS main; +EXEC SQL CONNECT TO "connectdb" AS second; +EXEC SQL CONNECT TO "unix:postgresql://200.46.204.71/connectdb" AS main USER connectuser; +EXEC SQL CONNECT TO "unix:postgresql://localhost/connectdb" AS main USER connectuser; +EXEC SQL CONNECT TO 'connectdb' AS main; +EXEC SQL CONNECT TO 'unix:postgresql://localhost/connectdb' AS main USER :user; +EXEC SQL CONNECT TO :db AS :id; +EXEC SQL CONNECT TO :db USER connectuser USING :pw; +EXEC SQL CONNECT TO @localhost AS main USER connectdb; +EXEC SQL CONNECT TO REGRESSDB1 as main; +EXEC SQL CONNECT TO AS main USER connectdb; +EXEC SQL CONNECT TO connectdb AS :id; +EXEC SQL CONNECT TO connectdb AS main USER connectuser/connectdb; +EXEC SQL CONNECT TO connectdb AS main; +EXEC SQL CONNECT TO connectdb@localhost AS main; +EXEC SQL CONNECT TO tcp:postgresql://localhost/ USER connectdb; +EXEC SQL CONNECT TO tcp:postgresql://localhost/connectdb USER connectuser IDENTIFIED BY connectpw; +EXEC SQL CONNECT TO tcp:postgresql://localhost:20/connectdb USER connectuser IDENTIFIED BY connectpw; +EXEC SQL CONNECT TO unix:postgresql://localhost/ AS main USER connectdb; +EXEC SQL CONNECT TO unix:postgresql://localhost/connectdb AS main USER connectuser; +EXEC SQL CONNECT TO unix:postgresql://localhost/connectdb USER connectuser IDENTIFIED BY "connectpw"; +EXEC SQL CONNECT TO unix:postgresql://localhost/connectdb USER connectuser USING "connectpw"; +EXEC SQL CONNECT TO unix:postgresql://localhost/connectdb?connect_timeout=14 USER connectuser; + + + + + Here is an example program that illustrates the use of host + variables to specify connection parameters: + +int +main(void) +{ +EXEC SQL BEGIN DECLARE SECTION; + char *dbname = "testdb"; /* database name */ + char *user = "testuser"; /* connection user name */ + char *connection = "tcp:postgresql://localhost:5432/testdb"; + /* connection string */ + char ver[256]; /* buffer to store the version string */ +EXEC SQL END DECLARE SECTION; + + ECPGdebug(1, stderr); + + EXEC SQL CONNECT TO :dbname USER :user; + EXEC SQL SELECT version() INTO :ver; + EXEC SQL DISCONNECT; + + printf("version: %s\n", ver); + + EXEC SQL CONNECT TO :connection USER :user; + EXEC SQL SELECT version() INTO :ver; + EXEC SQL DISCONNECT; + + printf("version: %s\n", ver); + + return 0; +} + + + + + + Compatibility + + + CONNECT is specified in the SQL standard, but + the format of the connection parameters is + implementation-specific. + + + + + See Also + + + + + + + + + + + DEALLOCATE DESCRIPTOR + deallocate an SQL descriptor area + + + + +DEALLOCATE DESCRIPTOR name + + + + + Description + + + DEALLOCATE DESCRIPTOR deallocates a named SQL + descriptor area. + + + + + Parameters + + + + name + + + The name of the descriptor which is going to be deallocated. + It is case sensitive. This can be an SQL identifier or a host + variable. + + + + + + + + Examples + + +EXEC SQL DEALLOCATE DESCRIPTOR mydesc; + + + + + Compatibility + + + DEALLOCATE DESCRIPTOR is specified in the SQL + standard. + + + + + See Also + + + + + + + + + + + + DECLARE + define a cursor + + + + +DECLARE cursor_name [ BINARY ] [ INSENSITIVE ] [ [ NO ] SCROLL ] CURSOR [ { WITH | WITHOUT } HOLD ] FOR prepared_name +DECLARE cursor_name [ BINARY ] [ INSENSITIVE ] [ [ NO ] SCROLL ] CURSOR [ { WITH | WITHOUT } HOLD ] FOR query + + + + + Description + + + DECLARE declares a cursor for iterating over + the result set of a prepared statement. This command has + slightly different semantics from the direct SQL + command DECLARE: Whereas the latter executes a + query and prepares the result set for retrieval, this embedded + SQL command merely declares a name as a loop + variable for iterating over the result set of a query; + the actual execution happens when the cursor is opened with + the OPEN command. + + + + + Parameters + + + + cursor_name + + + A cursor name, case sensitive. This can be an SQL identifier + or a host variable. + + + + + + prepared_name + + + The name of a prepared query, either as an SQL identfier or a + host variable. + + + + + + query + + + A or + command which will provide the + rows to be returned by the cursor. + + + + + + + For the meaning of the cursor options, + see . + + + + + Examples + + + Examples declaring a cursor for a query: + +EXEC SQL DECLARE C CURSOR FOR SELECT * FROM My_Table; +EXEC SQL DECLARE C CURSOR FOR SELECT Item1 FROM T; +EXEC SQL DECLARE cur1 CURSOR FOR SELECT version(); + + + + + An example declaring a cursor for a prepared statement: + +EXEC SQL PREPARE stmt1 AS SELECT version(); +EXEC SQL DECLARE cur1 CURSOR FOR stmt1; + + + + + + Compatibility + + + DECLARE is specified in the SQL standard. + + + + + See Also + + + + + + + + + + + + DESCRIBE + obtain information about a prepared statement or result set + + + + +DESCRIBE [ OUTPUT ] prepared_name USING [ SQL ] DESCRIPTOR descriptor_name +DESCRIBE [ OUTPUT ] prepared_name INTO [ SQL ] DESCRIPTOR descriptor_name +DESCRIBE [ OUTPUT ] prepared_name INTO sqlda_name + + + + + Description + + + DECLARE retrieves metadata information about + the result columns contained in a prepared statement, without + actually fetching a row. + + + + + Parameters + + + + prepared_name + + + The name of a prepared statement. This can be an SQL + identifier or a host variable. + + + + + + descriptor_name + + + A descriptor name. It is case sensitive. It can be an SQL + identifier or a host variable. + + + + + + sqlda_name + + + The name of an SQLDA variable. + + + + + + + + Examples + + +EXEC SQL ALLOCATE DESCRIPTOR mydesc; +EXEC SQL PREPARE stmt1 FROM :sql_stmt; +EXEC SQL DESCRIBE stmt1 INTO SQL DESCRIPTOR mydesc; +EXEC SQL GET DESCRIPTOR mydesc VALUE 1 :charvar = NAME; +EXEC SQL DEALLOCATE DESCRIPTOR mydesc; + + + + + Compatibility + + + DESCRIBE is specified in the SQL standard. + + + + + See Also + + + + + + + + + + + DISCONNECT + terminate a database connection + + + + +DISCONNECT connection_name +DISCONNECT [ CURRENT ] +DISCONNECT DEFAULT +DISCONNECT ALL + + + + + Description + + + DISCONNECT closes a connection (or all + connections) to the database. + + + + + Parameters + + + + connection_name + + + A database connection name established by + the CONNECT command. + + + + + + CURRENT + + + Close the current connection, which is either + the most recently opened connection, or the connection set by + the SET CONNECTION command. This is also + the default if no argument is given to + the DISCONNECT command. + + + + + + DEFAULT + + + Close the default connection. + + + + + + ALL + + + Close all open connections. + + + + + + + + Examples + + +int +main(void) +{ + EXEC SQL CONNECT TO testdb AS DEFAULT USER testuser; + EXEC SQL CONNECT TO testdb AS con1 USER testuser; + EXEC SQL CONNECT TO testdb AS con2 USER testuser; + EXEC SQL CONNECT TO testdb AS con3 USER testuser; + + EXEC SQL DISCONNECT CURRENT; /* close con3 */ + EXEC SQL DISCONNECT DEFAULT; /* close DEFAULT */ + EXEC SQL DISCONNECT ALL; /* close con2 and con1 */ + + return 0; +} + + + + + Compatibility + + + DISCONNECT is specified in the SQL standard. + + + + + See Also + + + + + + + + + + + EXECUTE IMMEDIATE + dynamically prepare and execute a statement + + + + +EXECUTE IMMEDIATE string + + + + + Description + + + EXECUTE IMMEDIATE immediately prepares and + executes a dynamically specified SQL statement, without + retrieving result rows. + + + + + Parameters + + + + string + + + A literal C string or a host variable containing the SQL + statement to be executed. + + + + + + + + Examples + + + Here is an example that executes an INSERT + statement using EXECUTE IMMEDIATE and a host + variable named command: + +sprintf(command, "INSERT INTO test (name, amount, letter) VALUES ('db: ''r1''', 1, 'f')"); +EXEC SQL EXECUTE IMMEDIATE :command; + + + + + + Compatibility + + + EXECUTE IMMEDIATE is specified in the SQL standard. + + + + + + + GET DESCRIPTOR + get information from an SQL descriptor area + + + + +GET DESCRIPTOR descriptor_name :cvariable = descriptor_header_item [, ... ] +GET DESCRIPTOR descriptor_name VALUE column_number :cvariable = descriptor_item [, ... ] + + + + + Description + + + GET DESCRIPTOR retrieves information about a + query result set from an SQL descriptor area and stores it into + host variables. A descriptor area is typically populated + using FETCH or SELECT + before using this command to transfer the information into host + language variables. + + + + This command has two forms: The first form retrieves + descriptor header items, which apply to the result + set in its entirety. One example is the row count. The second + form, which requires the column number as additional parameter, + retrieves information about a particular column. Examples are + the column name and the actual column value. + + + + + Parameters + + + + descriptor_name + + + A descriptor name. + + + + + + descriptor_header_item + + + A token identifying which header information item to retrieve. + Only COUNT, to get the number of columns in the + result set, is currently supported. + + + + + + column_number + + + The number of the column about which information is to be + retrieved. The count starts at 1. + + + + + + descriptor_item + + + A token identifying which item of information about a column + to retrieve. See for + a list of supported items. + + + + + + cvariable + + + A host variable that will receive the data retrieved from the + descriptor area. + + + + + + + + Examples + + + An example to retrieve the number of columns in a result set: + +EXEC SQL GET DESCRIPTOR d :d_count = COUNT; + + + + + An example to retrieve a data length in the first column: + +EXEC SQL GET DESCRIPTOR d VALUE 1 :d_returned_octet_length = RETURNED_OCTET_LENGTH; + + + + + An example to retrieve the data body of the second column as a + string: + +EXEC SQL GET DESCRIPTOR d VALUE 2 :d_data = DATA; + + + + + Here is an example for a whole procedure of + executing SELECT current_database(); and showing the number of + columns, the column data length, and the column data: + +int +main(void) +{ +EXEC SQL BEGIN DECLARE SECTION; + int d_count; + char d_data[1024]; + int d_returned_octet_length; +EXEC SQL END DECLARE SECTION; + + EXEC SQL CONNECT TO testdb AS con1 USER testuser; + EXEC SQL ALLOCATE DESCRIPTOR d; + + /* Declare, open a cursor, and assign a descriptor to the cursor */ + EXEC SQL DECLARE cur CURSOR FOR SELECT current_database(); + EXEC SQL OPEN cur; + EXEC SQL FETCH NEXT FROM cur INTO SQL DESCRIPTOR d; + + /* Get a number of total columns */ + EXEC SQL GET DESCRIPTOR d :d_count = COUNT; + printf("d_count = %d\n", d_count); + + /* Get length of a returned column */ + EXEC SQL GET DESCRIPTOR d VALUE 1 :d_returned_octet_length = RETURNED_OCTET_LENGTH; + printf("d_returned_octet_length = %d\n", d_returned_octet_length); + + /* Fetch the returned column as a string */ + EXEC SQL GET DESCRIPTOR d VALUE 1 :d_data = DATA; + printf("d_data = %s\n", d_data); + + /* Closing */ + EXEC SQL CLOSE cur; + EXEC SQL COMMIT; + + EXEC SQL DEALLOCATE DESCRIPTOR d; + EXEC SQL DISCONNECT ALL; + + return 0; +} + + When the example is executed, the result will look like this: + +d_count = 1 +d_returned_octet_length = 6 +d_data = testdb + + + + + + Compatibility + + + GET DESCRIPTOR is specified in the SQL standard. + + + + + See Also + + + + + + + + + + + OPEN + open a dynamic cursor + + + + +OPEN cursor_name +OPEN cursor_name USING value [, ... ] +OPEN cursor_name USING SQL DESCRIPTOR descriptor_name + + + + + Description + + + OPEN opens a cursor and optionally binds + actual values to the placeholders in the cursor's declaration. + The cursor must previously have been declared with + the DECLARE command. The execution + of OPEN causes the query to start executing on + the server. + + + + + Parameters + + + + cursor_name + + + The name of the cursor to be opened. This can be an SQL + identifier or a host variable. + + + + + + value + + + A value to be bound to a placeholder in the cursor. This can + be an SQL constant, a host variable, or a host variable with + indicator. + + + + + + descriptor_name + + + The name of a descriptor containing values to be bound to the + placeholders in the cursor. This can be an SQL identifier or + a host variable. + + + + + + + + Examples + + +EXEC SQL OPEN a; +EXEC SQL OPEN d USING 1, 'test'; +EXEC SQL OPEN c1 USING SQL DESCRIPTOR mydesc; +EXEC SQL OPEN :curname1; + + + + + Compatibility + + + OPEN is specified in the SQL standard. + + + + + See Also + + + + + + + + + + + PREPARE + prepare a statement for execution + + + + +PREPARE name FROM string + + + + + Description + + + PREPARE prepares a statement dynamically + specified as a string for execution. This is different from the + direct SQL statement , which can also + be used in embedded programs. The + command is used to execute either kind of prepared statement. + + + + + Parameters + + + + prepared_name + + + An identifier for the prepared query. + + + + + + string + + + A literal C string or a host variable containing a preparable + statement, one of the SELECT, INSERT, UPDATE, or + DELETE. + + + + + + + + Examples + +char *stmt = "SELECT * FROM test1 WHERE a = ? AND b = ?"; + +EXEC SQL ALLOCATE DESCRIPTOR outdesc; +EXEC SQL PREPARE foo FROM :stmt; + +EXEC SQL EXECUTE foo USING SQL DESCRIPTOR indesc INTO SQL DESCRIPTOR outdesc; + + + + + Compatibility + + + PREPARE is specified in the SQL standard. + + + + + See Also + + + + + + + + + + SET AUTOCOMMIT + set the autocommit behavior of the current session + + + + +SET AUTOCOMMIT { = | TO } { ON | OFF } + + + + + Description + + + SET AUTOCOMMIT sets the autocommit behavior of + the current database session. By default, embedded SQL programs + are not in autocommit mode, + so COMMIT needs to be issued explicitly when + desired. This command can change the session to autocommit mode, + where each individual statement is committed implicitly. + + + + + Compatibility + + + SET AUTOCOMMIT is an extension of PostgreSQL ECPG. + + + + + + + SET CONNECTION + select a database connection + + + + +SET CONNECTION [ TO | = ] connection_name + + + + + Description + + + SET CONNECTION sets the current + database connection, which is the one that all commands use + unless overridden. + + + + + Parameters + + + + connection_name + + + A database connection name established by + the CONNECT command. + + + + + + DEFAULT + + + Set the connection to the default connection. + + + + + + + + Examples + + +EXEC SQL SET CONNECTION TO con2; +EXEC SQL SET CONNECTION = con1; + + + + + Compatibility + + + SET CONNECTION is specified in the SQL standard. + + + + + See Also + + + + + + + + + + + SET DESCRIPTOR + set information in an SQL descriptor area + + + + +SET DESCRIPTOR descriptor_name descriptor_header_item = value [, ... ] +SET DESCRIPTOR descriptor_name VALUE number descriptor_item = value [, ...] + + + + + Description + + + SET DESCRIPTOR populates an SQL descriptor + area with values. The descriptor area is then typically used to + bind parameters in a prepared query execution. + + + + This command has two forms: The first form applies to the + descriptor header, which is independent of a + particular datum. The second form assigns values to particular + datums, identified by number. + + + + + Parameters + + + + descriptor_name + + + A descriptor name. + + + + + + descriptor_header_item + + + A token identifying which header information item to set. + Only COUNT, to set the number of descriptor + items, is currently supported. + + + + + + number + + + The number of the descriptor item to set. The count starts at + 1. + + + + + + descriptor_item + + + A token identifiying which item of information to set in the + descriptor. See for a + list of supported items. + + + + + + value + + + A value to store into the descriptor item. This can be an SQL + constant or a host variable. + + + + + + + + Examples + +EXEC SQL SET DESCRIPTOR indesc COUNT = 1; +EXEC SQL SET DESCRIPTOR indesc VALUE 1 DATA = 2; +EXEC SQL SET DESCRIPTOR indesc VALUE 1 DATA = :val1; +EXEC SQL SET DESCRIPTOR indesc VALUE 2 INDICATOR = :val1, DATA = 'some string'; +EXEC SQL SET DESCRIPTOR indesc VALUE 2 INDICATOR = :val2null, DATA = :val2; + + + + + Compatibility + + + SET DESCRIPTOR is specified in the SQL standard. + + + + + See Also + + + + + + + + + + + TYPE + define a new data type + + + + +TYPE type_name IS ctype + + + + + Description + + + The TYPE command defines a new C type. It is + equivalent to putting a typedef into a declare + section. + + + + This command is only recognized when ecpg is + run with the option. + + + + + Parameters + + + + type_name + + + The name for the new type. It must be a valid C type name. + + + + + + ctype + + + A C type specification. + + + + + + + + Examples + + +EXEC SQL TYPE customer IS + struct + { + varchar name[50]; + int phone; + }; + +EXEC SQL TYPE cust_ind IS + struct ind + { + short name_ind; + short phone_ind; + }; + +EXEC SQL TYPE c IS char reference; +EXEC SQL TYPE ind IS union { int integer; short smallint; }; +EXEC SQL TYPE intarray IS int[AMOUNT]; +EXEC SQL TYPE str IS varchar[BUFFERSIZ]; +EXEC SQL TYPE string IS char[11]; + + + + Here is an example program that uses EXEC SQL + TYPE: + +EXEC SQL WHENEVER SQLERROR SQLPRINT; + +EXEC SQL TYPE tt IS + struct + { + varchar v[256]; + int i; + }; + +EXEC SQL TYPE tt_ind IS + struct ind { + short v_ind; + short i_ind; + }; + +int +main(void) +{ +EXEC SQL BEGIN DECLARE SECTION; + tt t; + tt_ind t_ind; +EXEC SQL END DECLARE SECTION; + + EXEC SQL CONNECT TO testdb AS con1; + + EXEC SQL SELECT current_database(), 256 INTO :t:t_ind LIMIT 1; + + printf("t.v = %s\n", t.v.arr); + printf("t.i = %d\n", t.i); + + printf("t_ind.v_ind = %d\n", t_ind.v_ind); + printf("t_ind.i_ind = %d\n", t_ind.i_ind); + + EXEC SQL DISCONNECT con1; + + return 0; +} + + + The output from this program looks like this: + +t.v = testdb +t.i = 256 +t_ind.v_ind = 0 +t_ind.i_ind = 0 + + + + + + Compatibility + + + The TYPE command is a PostgreSQL extension. + + + + + + + VAR + define a variable + + + + +VAR varname IS ctype + + + + + Description + + + The VAR command defines a host variable. It + is equivalent to an ordinary C variable definition inside a + declare section. + + + + + Parameters + + + + varname + + + A C variable name. + + + + + + ctype + + + A C type specification. + + + + + + + + Examples + + +EXEC SQL VAR vc IS VARCHAR[10]; +EXEC SQL VAR boolvar IS bool; + + + + + Compatibility + + + The VAR command is a PostgreSQL extension. + + + + + + + WHENEVER + specify the action to be taken when an SQL statement causes a specific class condition to be raised + + + + +WHENEVER { NOT FOUND | SQLERROR | SQLWARNING } action + + + + + Description + + + Define a behavior which is called on the special cases (Rows not + found, SQL warnings or errors) in the result of SQL execution. + + + + + Parameters + + + See for a description of the + parameters. + + + + + Examples + + +EXEC SQL WHENEVER NOT FOUND CONTINUE; +EXEC SQL WHENEVER NOT FOUND DO BREAK; +EXEC SQL WHENEVER SQLWARNING SQLPRINT; +EXEC SQL WHENEVER SQLWARNING DO warn(); +EXEC SQL WHENEVER SQLERROR sqlprint; +EXEC SQL WHENEVER SQLERROR CALL print2(); +EXEC SQL WHENEVER SQLERROR DO handle_error("select"); +EXEC SQL WHENEVER SQLERROR DO sqlnotice(NULL, NONO); +EXEC SQL WHENEVER SQLERROR DO sqlprint(); +EXEC SQL WHENEVER SQLERROR GOTO error_label; +EXEC SQL WHENEVER SQLERROR STOP; + + + + A typical application is the use of WHENEVER NOT FOUND + BREAK to handle looping through result sets: + +int +main(void) +{ + EXEC SQL CONNECT TO testdb AS con1; + EXEC SQL ALLOCATE DESCRIPTOR d; + EXEC SQL DECLARE cur CURSOR FOR SELECT current_database(), 'hoge', 256; + EXEC SQL OPEN cur; + + /* when end of result set reached, break out of while loop */ + EXEC SQL WHENEVER NOT FOUND DO BREAK; + + while (1) + { + EXEC SQL FETCH NEXT FROM cur INTO SQL DESCRIPTOR d; + ... + } + + EXEC SQL CLOSE cur; + EXEC SQL COMMIT; + + EXEC SQL DEALLOCATE DESCRIPTOR d; + EXEC SQL DISCONNECT ALL; + + return 0; +} + + + + + + Compatibility + + + WHENEVER is specified in the SQL standard, but + most of the actions are PostgreSQL extensions. + + + - <productname>Informix</productname> compatibility mode + <productname>Informix</productname> Compatibility Mode ecpg can be run in a so-called Informix compatibility mode. If this mode is active, it tries to behave as if it were the Informix @@ -2866,6 +7835,17 @@ $INSERT INTO test(i, j) VALUES (7, :j); $COMMIT; + + + + There must not be any white space between the $ + and a following preprocessor directive, that is, + include, define, ifdef, + etc. Otherwise, the preprocessor will parse the token as a host + variable. + + + There are two compatibility modes: INFORMIX, INFORMIX_SE @@ -2893,7 +7873,7 @@ $COMMIT; find support in ECPG for that either. - + Additional types The Informix-special "string" pseudo-type for storing right-trimmed character string data is now @@ -2909,7 +7889,7 @@ EXEC SQL FETCH MYCUR INTO :userid; - + Additional/missing embedded SQL statements @@ -2944,51 +7924,50 @@ EXEC SQL CLOSE DATABASE; FREE statement_name is a synonym for DEALLOCATE PREPARE statement_name. - - + + - - Informix-compatible SQLDA Descriptor Areas + + Informix-compatible SQLDA descriptor areas Informix-compatible mode supports a different structure than the one described in . See below: struct sqlvar_compat { - short sqltype; - int sqllen; - char *sqldata; - short *sqlind; - char *sqlname; - char *sqlformat; - short sqlitype; - short sqlilen; - char *sqlidata; - int sqlxid; - char *sqltypename; - short sqltypelen; - short sqlownerlen; - short sqlsourcetype; - char *sqlownername; - int sqlsourceid; - - char *sqlilongdata; - int sqlflags; - void *sqlreserved; + short sqltype; + int sqllen; + char *sqldata; + short *sqlind; + char *sqlname; + char *sqlformat; + short sqlitype; + short sqlilen; + char *sqlidata; + int sqlxid; + char *sqltypename; + short sqltypelen; + short sqlownerlen; + short sqlsourcetype; + char *sqlownername; + int sqlsourceid; + char *sqlilongdata; + int sqlflags; + void *sqlreserved; }; struct sqlda_compat { - short sqld; - struct sqlvar_compat *sqlvar; - char desc_name[19]; - short desc_occ; - struct sqlda_compat *desc_next; - void *reserved; + short sqld; + struct sqlvar_compat *sqlvar; + char desc_name[19]; + short desc_occ; + struct sqlda_compat *desc_next; + void *reserved; }; typedef struct sqlvar_compat sqlvar_t; @@ -2998,7 +7977,7 @@ typedef struct sqlda_compat sqlda_t; The global properties are: - + sqld @@ -3010,7 +7989,7 @@ typedef struct sqlda_compat sqlda_t; - sqlvar + sqlvar Pointer to the per-field properties. @@ -3229,7 +8208,7 @@ EXEC SQL INCLUDE sqlda.h; - + Additional functions @@ -3245,7 +8224,7 @@ int decadd(decimal *arg1, decimal *arg2, decimal *sum); (arg1), a pointer to the second operand of type decimal (arg2) and a pointer to a value of type decimal that will contain the sum (sum). On success, the function returns 0. - ECPG_INFORMIX_NUM_OVERFLOW is returned in case of overflow and + ECPG_INFORMIX_NUM_OVERFLOW is returned in case of overflow and ECPG_INFORMIX_NUM_UNDERFLOW in case of underflow. -1 is returned for other failures and errno is set to the respective errno number of the pgtypeslib. @@ -4287,7 +9266,7 @@ risnull(CINTTYPE, (char *) &i); - + Additional constants Note that all constants here describe errors and all of them are defined @@ -4450,1102 +9429,6 @@ risnull(CINTTYPE, (char *) &i); - - Error Handling - - - This section describes how you can handle exceptional conditions - and warnings in an embedded SQL program. There are several - nonexclusive facilities for this. - - - - Setting Callbacks - - - One simple method to catch errors and warnings is to set a - specific action to be executed whenever a particular condition - occurs. In general: - -EXEC SQL WHENEVER condition action; - - - - - condition can be one of the following: - - - - SQLERROR - - - The specified action is called whenever an error occurs during - the execution of an SQL statement. - - - - - - SQLWARNING - - - The specified action is called whenever a warning occurs - during the execution of an SQL statement. - - - - - - NOT FOUND - - - The specified action is called whenever an SQL statement - retrieves or affects zero rows. (This condition is not an - error, but you might be interested in handling it specially.) - - - - - - - - action can be one of the following: - - - - CONTINUE - - - This effectively means that the condition is ignored. This is - the default. - - - - - - GOTO label - GO TO label - - - Jump to the specified label (using a C goto - statement). - - - - - - SQLPRINT - - - Print a message to standard error. This is useful for simple - programs or during prototyping. The details of the message - cannot be configured. - - - - - - STOP - - - Call exit(1), which will terminate the - program. - - - - - - DO BREAK - - - Execute the C statement break. This should - only be used in loops or switch statements. - - - - - - CALL name (args) - DO name (args) - - - Call the specified C functions with the specified arguments. - - - - - - The SQL standard only provides for the actions - CONTINUE and GOTO (and - GO TO). - - - - Here is an example that you might want to use in a simple program. - It prints a simple message when a warning occurs and aborts the - program when an error happens: - -EXEC SQL WHENEVER SQLWARNING SQLPRINT; -EXEC SQL WHENEVER SQLERROR STOP; - - - - - The statement EXEC SQL WHENEVER is a directive - of the SQL preprocessor, not a C statement. The error or warning - actions that it sets apply to all embedded SQL statements that - appear below the point where the handler is set, unless a - different action was set for the same condition between the first - EXEC SQL WHENEVER and the SQL statement causing - the condition, regardless of the flow of control in the C program. - So neither of the two following C program excerpts will have the - desired effect: - -/* - * WRONG - */ -int main(int argc, char *argv[]) -{ - ... - if (verbose) { - EXEC SQL WHENEVER SQLWARNING SQLPRINT; - } - ... - EXEC SQL SELECT ...; - ... -} - - - -/* - * WRONG - */ -int main(int argc, char *argv[]) -{ - ... - set_error_handler(); - ... - EXEC SQL SELECT ...; - ... -} - -static void set_error_handler(void) -{ - EXEC SQL WHENEVER SQLERROR STOP; -} - - - - - - sqlca - - - For more powerful error handling, the embedded SQL interface - provides a global variable with the name sqlca - that has the following structure: - -struct -{ - char sqlcaid[8]; - long sqlabc; - long sqlcode; - struct - { - int sqlerrml; - char sqlerrmc[SQLERRMC_LEN]; - } sqlerrm; - char sqlerrp[8]; - long sqlerrd[6]; - char sqlwarn[8]; - char sqlstate[5]; -} sqlca; - - (In a multithreaded program, every thread automatically gets its - own copy of sqlca. This works similarly to the - handling of the standard C global variable - errno.) - - - - sqlca covers both warnings and errors. If - multiple warnings or errors occur during the execution of a - statement, then sqlca will only contain - information about the last one. - - - - If no error occurred in the last SQL statement, - sqlca.sqlcode will be 0 and - sqlca.sqlstate will be - "00000". If a warning or error occurred, then - sqlca.sqlcode will be negative and - sqlca.sqlstate will be different from - "00000". A positive - sqlca.sqlcode indicates a harmless condition, - such as that the last query returned zero rows. - sqlcode and sqlstate are two - different error code schemes; details appear below. - - - - If the last SQL statement was successful, then - sqlca.sqlerrd[1] contains the OID of the - processed row, if applicable, and - sqlca.sqlerrd[2] contains the number of - processed or returned rows, if applicable to the command. - - - - In case of an error or warning, - sqlca.sqlerrm.sqlerrmc will contain a string - that describes the error. The field - sqlca.sqlerrm.sqlerrml contains the length of - the error message that is stored in - sqlca.sqlerrm.sqlerrmc (the result of - strlen(), not really interesting for a C - programmer). Note that some messages are too long to fit in the - fixed-size sqlerrmc array; they will be truncated. - - - - In case of a warning, sqlca.sqlwarn[2] is set - to W. (In all other cases, it is set to - something different from W.) If - sqlca.sqlwarn[1] is set to - W, then a value was truncated when it was - stored in a host variable. sqlca.sqlwarn[0] is - set to W if any of the other elements are set - to indicate a warning. - - - - The fields sqlcaid, - sqlcabc, - sqlerrp, and the remaining elements of - sqlerrd and - sqlwarn currently contain no useful - information. - - - - The structure sqlca is not defined in the SQL - standard, but is implemented in several other SQL database - systems. The definitions are similar at the core, but if you want - to write portable applications, then you should investigate the - different implementations carefully. - - - - - <literal>SQLSTATE</literal> vs <literal>SQLCODE</literal> - - - The fields sqlca.sqlstate and - sqlca.sqlcode are two different schemes that - provide error codes. Both are derived from the SQL standard, but - SQLCODE has been marked deprecated in the SQL-92 - edition of the standard and has been dropped in later editions. - Therefore, new applications are strongly encouraged to use - SQLSTATE. - - - - SQLSTATE is a five-character array. The five - characters contain digits or upper-case letters that represent - codes of various error and warning conditions. - SQLSTATE has a hierarchical scheme: the first - two characters indicate the general class of the condition, the - last three characters indicate a subclass of the general - condition. A successful state is indicated by the code - 00000. The SQLSTATE codes are for - the most part defined in the SQL standard. The - PostgreSQL server natively supports - SQLSTATE error codes; therefore a high degree - of consistency can be achieved by using this error code scheme - throughout all applications. For further information see - . - - - - SQLCODE, the deprecated error code scheme, is a - simple integer. A value of 0 indicates success, a positive value - indicates success with additional information, a negative value - indicates an error. The SQL standard only defines the positive - value +100, which indicates that the last command returned or - affected zero rows, and no specific negative values. Therefore, - this scheme can only achieve poor portability and does not have a - hierarchical code assignment. Historically, the embedded SQL - processor for PostgreSQL has assigned - some specific SQLCODE values for its use, which - are listed below with their numeric value and their symbolic name. - Remember that these are not portable to other SQL implementations. - To simplify the porting of applications to the - SQLSTATE scheme, the corresponding - SQLSTATE is also listed. There is, however, no - one-to-one or one-to-many mapping between the two schemes (indeed - it is many-to-many), so you should consult the global - SQLSTATE listing in - in each case. - - - - These are the assigned SQLCODE values: - - - - 0 (ECPG_NO_ERROR) - - - Indicates no error. (SQLSTATE 00000) - - - - - - 100 (ECPG_NOT_FOUND) - - - This is a harmless condition indicating that the last command - retrieved or processed zero rows, or that you are at the end of - the cursor. (SQLSTATE 02000) - - - - - - -12 (ECPG_OUT_OF_MEMORY) - - - Indicates that your virtual memory is exhausted. The numeric - value is defined as -ENOMEM. (SQLSTATE - YE001) - - - - - - -200 (ECPG_UNSUPPORTED) - - - Indicates the preprocessor has generated something that the - library does not know about. Perhaps you are running - incompatible versions of the preprocessor and the - library. (SQLSTATE YE002) - - - - - - -201 (ECPG_TOO_MANY_ARGUMENTS) - - - This means that the command specified more host variables than - the command expected. (SQLSTATE 07001 or 07002) - - - - - - -202 (ECPG_TOO_FEW_ARGUMENTS) - - - This means that the command specified fewer host variables than - the command expected. (SQLSTATE 07001 or 07002) - - - - - - -203 (ECPG_TOO_MANY_MATCHES) - - - This means a query has returned multiple rows but the statement - was only prepared to store one result row (for example, because - the specified variables are not arrays). (SQLSTATE 21000) - - - - - - -204 (ECPG_INT_FORMAT) - - - The host variable is of type int and the datum in - the database is of a different type and contains a value that - cannot be interpreted as an int. The library uses - strtol() for this conversion. (SQLSTATE - 42804) - - - - - - -205 (ECPG_UINT_FORMAT) - - - The host variable is of type unsigned int and the - datum in the database is of a different type and contains a - value that cannot be interpreted as an unsigned - int. The library uses strtoul() - for this conversion. (SQLSTATE 42804) - - - - - - -206 (ECPG_FLOAT_FORMAT) - - - The host variable is of type float and the datum - in the database is of another type and contains a value that - cannot be interpreted as a float. The library - uses strtod() for this conversion. - (SQLSTATE 42804) - - - - - - -207 (ECPG_NUMERIC_FORMAT) - - - The host variable is of type numeric and the datum - in the database is of another type and contains a value that - cannot be interpreted as a numeric value. - (SQLSTATE 42804) - - - - - - -208 (ECPG_INTERVAL_FORMAT) - - - The host variable is of type interval and the datum - in the database is of another type and contains a value that - cannot be interpreted as an interval value. - (SQLSTATE 42804) - - - - - - -209 (ECPG_DATE_FORMAT) - - - The host variable is of type date and the datum in - the database is of another type and contains a value that - cannot be interpreted as a date value. - (SQLSTATE 42804) - - - - - - -210 (ECPG_TIMESTAMP_FORMAT) - - - The host variable is of type timestamp and the - datum in the database is of another type and contains a value - that cannot be interpreted as a timestamp value. - (SQLSTATE 42804) - - - - - - -211 (ECPG_CONVERT_BOOL) - - - This means the host variable is of type bool and - the datum in the database is neither 't' nor - 'f'. (SQLSTATE 42804) - - - - - - -212 (ECPG_EMPTY) - - - The statement sent to the PostgreSQL - server was empty. (This cannot normally happen in an embedded - SQL program, so it might point to an internal error.) (SQLSTATE - YE002) - - - - - - -213 (ECPG_MISSING_INDICATOR) - - - A null value was returned and no null indicator variable was - supplied. (SQLSTATE 22002) - - - - - - -214 (ECPG_NO_ARRAY) - - - An ordinary variable was used in a place that requires an - array. (SQLSTATE 42804) - - - - - - -215 (ECPG_DATA_NOT_ARRAY) - - - The database returned an ordinary variable in a place that - requires array value. (SQLSTATE 42804) - - - - - - - -216 (ECPG_ARRAY_INSERT) - - - The value could not be inserted into the array. (SQLSTATE - 42804) - - - -]]> - - - -220 (ECPG_NO_CONN) - - - The program tried to access a connection that does not exist. - (SQLSTATE 08003) - - - - - - -221 (ECPG_NOT_CONN) - - - The program tried to access a connection that does exist but is - not open. (This is an internal error.) (SQLSTATE YE002) - - - - - - -230 (ECPG_INVALID_STMT) - - - The statement you are trying to use has not been prepared. - (SQLSTATE 26000) - - - - - - -239 (ECPG_INFORMIX_DUPLICATE_KEY) - - - Duplicate key error, violation of unique constraint (Informix - compatibility mode). (SQLSTATE 23505) - - - - - - -240 (ECPG_UNKNOWN_DESCRIPTOR) - - - The descriptor specified was not found. The statement you are - trying to use has not been prepared. (SQLSTATE 33000) - - - - - - -241 (ECPG_INVALID_DESCRIPTOR_INDEX) - - - The descriptor index specified was out of range. (SQLSTATE - 07009) - - - - - - -242 (ECPG_UNKNOWN_DESCRIPTOR_ITEM) - - - An invalid descriptor item was requested. (This is an internal - error.) (SQLSTATE YE002) - - - - - - -243 (ECPG_VAR_NOT_NUMERIC) - - - During the execution of a dynamic statement, the database - returned a numeric value and the host variable was not numeric. - (SQLSTATE 07006) - - - - - - -244 (ECPG_VAR_NOT_CHAR) - - - During the execution of a dynamic statement, the database - returned a non-numeric value and the host variable was numeric. - (SQLSTATE 07006) - - - - - - -284 (ECPG_INFORMIX_SUBSELECT_NOT_ONE) - - - A result of the subquery is not single row (Informix - compatibility mode). (SQLSTATE 21000) - - - - - - -400 (ECPG_PGSQL) - - - Some error caused by the PostgreSQL - server. The message contains the error message from the - PostgreSQL server. - - - - - - -401 (ECPG_TRANS) - - - The PostgreSQL server signaled that - we cannot start, commit, or rollback the transaction. - (SQLSTATE 08007) - - - - - - -402 (ECPG_CONNECT) - - - The connection attempt to the database did not succeed. - (SQLSTATE 08001) - - - - - - -403 (ECPG_DUPLICATE_KEY) - - - Duplicate key error, violation of unique constraint. (SQLSTATE - 23505) - - - - - - -404 (ECPG_SUBSELECT_NOT_ONE) - - - A result for the subquery is not single row. (SQLSTATE 21000) - - - - - - - -600 (ECPG_WARNING_UNRECOGNIZED) - - - An unrecognized warning was received from the server. - - - - - - -601 (ECPG_WARNING_QUERY_IGNORED) - - - Current transaction is aborted. Queries are ignored until the - end of the transaction block. - - - -]]> - - - -602 (ECPG_WARNING_UNKNOWN_PORTAL) - - - An invalid cursor name was specified. (SQLSTATE 34000) - - - - - - -603 (ECPG_WARNING_IN_TRANSACTION) - - - Transaction is in progress. (SQLSTATE 25001) - - - - - - -604 (ECPG_WARNING_NO_TRANSACTION) - - - There is no active (in-progress) transaction. (SQLSTATE 25P01) - - - - - - -605 (ECPG_WARNING_PORTAL_EXISTS) - - - An existing cursor name was specified. (SQLSTATE 42P03) - - - - - - - - - - - Preprocessor directives - - - Including files - - - To include an external file into your embedded SQL program, use: - -EXEC SQL INCLUDE filename; - - The embedded SQL preprocessor will look for a file named - filename.h, - preprocess it, and include it in the resulting C output. Thus, - embedded SQL statements in the included file are handled correctly. - - - - Note that this is not the same as: - -#include <filename.h> - - because this file would not be subject to SQL command preprocessing. - Naturally, you can continue to use the C - #include directive to include other header - files. - - - - - The include file name is case-sensitive, even though the rest of - the EXEC SQL INCLUDE command follows the normal - SQL case-sensitivity rules. - - - - - - The #define and #undef directives - - Similar to the directive #define that is known from C, - embedded SQL has a similar concept: - -EXEC SQL DEFINE name; -EXEC SQL DEFINE name value; - - So you can define a name: - -EXEC SQL DEFINE HAVE_FEATURE; - - And you can also define constants: - -EXEC SQL DEFINE MYNUMBER 12; -EXEC SQL DEFINE MYSTRING 'abc'; - - Use undef to remove a previous definition: - -EXEC SQL UNDEF MYNUMBER; - - - - - Of course you can continue to use the C versions #define - and #undef in your embedded SQL program. The difference - is where your defined values get evaluated. If you use EXEC SQL - DEFINE then the ecpg preprocessor evaluates the defines and substitutes - the values. For example if you write: - -EXEC SQL DEFINE MYNUMBER 12; -... -EXEC SQL UPDATE Tbl SET col = MYNUMBER; - - then ecpg will already do the substitution and your C compiler will never - see any name or identifier MYNUMBER. Note that you cannot use - #define for a constant that you are going to use in an - embedded SQL query because in this case the embedded SQL precompiler is not - able to see this declaration. - - - - - ifdef, ifndef, else, elif, and endif directives - - You can use the following directives to compile code sections conditionally: - - - - EXEC SQL ifdef name; - - - Checks a name and processes subsequent lines if - name has been created with EXEC SQL define - name. - - - - - - EXEC SQL ifndef name; - - - Checks a name and processes subsequent lines if - name has not been created with - EXEC SQL define name. - - - - - - EXEC SQL else; - - - Starts processing an alternative section to a section introduced by - either EXEC SQL ifdef name or - EXEC SQL ifndef name. - - - - - - EXEC SQL elif name; - - - Checks name and starts an alternative section if - name has been created with EXEC SQL define - name. - - - - - - EXEC SQL endif; - - - Ends an alternative section. - - - - - - - - Example: - -EXEC SQL ifndef TZVAR; -EXEC SQL SET TIMEZONE TO 'GMT'; -EXEC SQL elif TZNAME; -EXEC SQL SET TIMEZONE TO TZNAME; -EXEC SQL else; -EXEC SQL SET TIMEZONE TO TZVAR; -EXEC SQL endif; - - - - - - - - Processing Embedded SQL Programs - - - Now that you have an idea how to form embedded SQL C programs, you - probably want to know how to compile them. Before compiling you - run the file through the embedded SQL - C preprocessor, which converts the - SQL statements you used to special function - calls. After compiling, you must link with a special library that - contains the needed functions. These functions fetch information - from the arguments, perform the SQL command using - the libpq interface, and put the result - in the arguments specified for output. - - - - The preprocessor program is called ecpg and is - included in a normal PostgreSQL installation. - Embedded SQL programs are typically named with an extension - .pgc. If you have a program file called - prog1.pgc, you can preprocess it by simply - calling: - -ecpg prog1.pgc - - This will create a file called prog1.c. If - your input files do not follow the suggested naming pattern, you - can specify the output file explicitly using the - option. - - - - The preprocessed file can be compiled normally, for example: - -cc -c prog1.c - - The generated C source files include header files from the - PostgreSQL installation, so if you installed - PostgreSQL in a location that is not searched by - default, you have to add an option such as - -I/usr/local/pgsql/include to the compilation - command line. - - - - To link an embedded SQL program, you need to include the - libecpg library, like so: - -cc -o myprog prog1.o prog2.o ... -lecpg - - Again, you might have to add an option like - -L/usr/local/pgsql/lib to that command line. - - - - If you manage the build process of a larger project using - make, it might be convenient to include - the following implicit rule to your makefiles: - -ECPG = ecpg - -%.c: %.pgc - $(ECPG) $< - - - - - The complete syntax of the ecpg command is - detailed in . - - - - The ecpg library is thread-safe by - default. However, you might need to use some threading - command-line options to compile your client code. - - - - - Library Functions - - - The libecpg library primarily contains - hidden functions that are used to implement the - functionality expressed by the embedded SQL commands. But there - are some functions that can usefully be called directly. Note that - this makes your code unportable. - - - - - - ECPGdebug(int on, FILE - *stream) turns on debug - logging if called with the first argument non-zero. Debug logging - is done on stream. The log contains - all SQL statements with all the input - variables inserted, and the results from the - PostgreSQL server. This can be very - useful when searching for errors in your SQL - statements. - - - - On Windows, if the ecpg libraries and an application are - compiled with different flags, this function call will crash the - application because the internal representation of the - FILE pointers differ. Specifically, - multithreaded/single-threaded, release/debug, and static/dynamic - flags should be the same for the library and all applications using - that library. - - - - - - - ECPGget_PGconn(const char *connection_name) - returns the library database connection handle identified by the given name. - If connection_name is set to NULL, the current - connection handle is returned. If no connection handle can be identified, the function returns - NULL. The returned connection handle can be used to call any other functions - from libpq, if necessary. - - - - It is a bad idea to manipulate database connection handles made from ecpg directly - with libpq routines. - - - - - - - ECPGtransactionStatus(const char *connection_name) - returns the current transaction status of the given connection identified by connection_name. - See and libpq's PQtransactionStatus() for details about the returned status codes. - - - - - - ECPGstatus(int lineno, - const char* connection_name) - returns true if you are connected to a database and false if not. - connection_name can be NULL - if a single connection is being used. - - - - - Internals diff --git a/doc/src/sgml/stylesheet-man.xsl b/doc/src/sgml/stylesheet-man.xsl index 81e875614a8..8c614ca754d 100644 --- a/doc/src/sgml/stylesheet-man.xsl +++ b/doc/src/sgml/stylesheet-man.xsl @@ -90,6 +90,50 @@ + + + + + + + + + + 0 + + + + + + + + + + + + + + + + + + + + + + + Note: + + + + + + +