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More minor updates and copy-editing.

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This commit is contained in:
Tom Lane
2004-12-30 21:45:37 +00:00
parent 1fbdb6bc9f
commit 883ac5ca7a
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doc/src/sgml/pltcl.sgml
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@@ -1,5 +1,5 @@
<!--
$PostgreSQL: pgsql/doc/src/sgml/pltcl.sgml,v 2.32 2004/11/21 21:17:02 tgl Exp $
$PostgreSQL: pgsql/doc/src/sgml/pltcl.sgml,v 2.33 2004/12/30 21:45:37 tgl Exp $
-->
<chapter id="pltcl">
@@ -16,7 +16,8 @@ $PostgreSQL: pgsql/doc/src/sgml/pltcl.sgml,v 2.32 2004/11/21 21:17:02 tgl Exp $
<para>
PL/Tcl is a loadable procedural language for the
<productname>PostgreSQL</productname> database system
that enables the Tcl language to be used to write functions and
that enables the <ulink url="http://www.tcl.tk/">Tcl</ulink>
language to be used to write functions and
trigger procedures.
</para>
@@ -59,7 +60,7 @@ $PostgreSQL: pgsql/doc/src/sgml/pltcl.sgml,v 2.32 2004/11/21 21:17:02 tgl Exp $
The shared object for the <application>PL/Tcl</> and <application>PL/TclU</> call handlers is
automatically built and installed in the
<productname>PostgreSQL</productname>
library directory if Tcl/Tk support is specified
library directory if Tcl support is specified
in the configuration step of the installation procedure. To install
<application>PL/Tcl</> and/or <application>PL/TclU</> in a particular database, use the
<command>createlang</command> program, for example
@@ -77,8 +78,7 @@ $PostgreSQL: pgsql/doc/src/sgml/pltcl.sgml,v 2.32 2004/11/21 21:17:02 tgl Exp $
To create a function in the <application>PL/Tcl</> language, use the standard syntax:
<programlisting>
CREATE FUNCTION <replaceable>funcname</replaceable>
(<replaceable>argument-types</replaceable>) RETURNS <replaceable>return-type</replaceable> AS $$
CREATE FUNCTION <replaceable>funcname</replaceable> (<replaceable>argument-types</replaceable>) RETURNS <replaceable>return-type</replaceable> AS $$
# PL/Tcl function body
$$ LANGUAGE pltcl;
</programlisting>
@@ -169,7 +169,16 @@ $$ LANGUAGE pltcl;
<para>
There is currently no support for returning a composite-type
result value.
result value, nor for returning sets.
</para>
<para>
<application>PL/Tcl</> does not currently have full support for
domain types: it treats a domain the same as the underlying scalar
type. This means that constraints associated with the domain will
not be enforced. This is not an issue for function arguments, but
it is a hazard if you declare a <application>PL/Tcl</> function
as returning a domain type.
</para>
</sect1>
@@ -180,10 +189,11 @@ $$ LANGUAGE pltcl;
<para>
The argument values supplied to a PL/Tcl function's code are simply
the input arguments converted to text form (just as if they had been
displayed by a <command>SELECT</> statement). Conversely, the <literal>return</>
displayed by a <command>SELECT</> statement). Conversely, the
<literal>return</>
command will accept any string that is acceptable input format for
the function's declared return type. So, the PL/Tcl programmer can
manipulate data values as if they were just text.
the function's declared return type. So, within the PL/Tcl function,
all values are just text strings.
</para>
</sect1>
@@ -215,9 +225,9 @@ $$ LANGUAGE pltcl;
command. The global name of this variable is the function's internal
name, and the local name is <literal>GD</>. It is recommended that
<literal>GD</> be used
for private data of a function. Use regular Tcl global variables
only for values that you specifically intend to be shared among multiple
functions.
for persistent private data of a function. Use regular Tcl global
variables only for values that you specifically intend to be shared among
multiple functions.
</para>
<para>
@@ -239,48 +249,48 @@ $$ LANGUAGE pltcl;
<term><literal><function>spi_exec</function> <optional role="tcl">-count <replaceable>n</replaceable></optional> <optional role="tcl">-array <replaceable>name</replaceable></optional> <replaceable>command</replaceable> <optional role="tcl"><replaceable>loop-body</replaceable></optional></literal></term>
<listitem>
<para>
Executes an SQL command given as a string. An error in the command
causes an error to be raised. Otherwise, the return value of <function>spi_exec</function>
is the number of rows processed (selected, inserted, updated, or
deleted) by the command, or zero if the command is a utility
statement. In addition, if the command is a <command>SELECT</> statement, the
values of the selected columns are placed in Tcl variables as
described below.
Executes an SQL command given as a string. An error in the command
causes an error to be raised. Otherwise, the return value of <function>spi_exec</function>
is the number of rows processed (selected, inserted, updated, or
deleted) by the command, or zero if the command is a utility
statement. In addition, if the command is a <command>SELECT</> statement, the
values of the selected columns are placed in Tcl variables as
described below.
</para>
<para>
The optional <literal>-count</> value tells
<function>spi_exec</function> the maximum number of rows
to process in the command. The effect of this is comparable to
setting up a query as a cursor and then saying <literal>FETCH <replaceable>n</></>.
The optional <literal>-count</> value tells
<function>spi_exec</function> the maximum number of rows
to process in the command. The effect of this is comparable to
setting up a query as a cursor and then saying <literal>FETCH <replaceable>n</></>.
</para>
<para>
If the command is a <command>SELECT</> statement, the values of the
result columns are placed into Tcl variables named after the columns.
If the command is a <command>SELECT</> statement, the values of the
result columns are placed into Tcl variables named after the columns.
If the <literal>-array</> option is given, the column values are
instead stored into the named associative array, with the
column names used as array indexes.
instead stored into the named associative array, with the
column names used as array indexes.
</para>
<para>
If the command is a <command>SELECT</> statement and no <replaceable>loop-body</>
script is given, then only the first row of results are stored into
Tcl variables; remaining rows, if any, are ignored. No storing occurs
if the
query returns no rows. (This case can be detected by checking the
result of <function>spi_exec</function>.) For example,
script is given, then only the first row of results are stored into
Tcl variables; remaining rows, if any, are ignored. No storing occurs
if the
query returns no rows. (This case can be detected by checking the
result of <function>spi_exec</function>.) For example,
<programlisting>
spi_exec "SELECT count(*) AS cnt FROM pg_proc"
</programlisting>
will set the Tcl variable <literal>$cnt</> to the number of rows in
the <structname>pg_proc</> system catalog.
will set the Tcl variable <literal>$cnt</> to the number of rows in
the <structname>pg_proc</> system catalog.
</para>
<para>
If the optional <replaceable>loop-body</> argument is given, it is
a piece of Tcl script that is executed once for each row in the
query result. (<replaceable>loop-body</> is ignored if the given
command is not a <command>SELECT</>.) The values of the current row's columns
are stored into Tcl variables before each iteration. For example,
a piece of Tcl script that is executed once for each row in the
query result. (<replaceable>loop-body</> is ignored if the given
command is not a <command>SELECT</>.) The values of the current row's columns
are stored into Tcl variables before each iteration. For example,
<programlisting>
spi_exec -array C "SELECT * FROM pg_class" {
@@ -288,14 +298,14 @@ spi_exec -array C "SELECT * FROM pg_class" {
}
</programlisting>
will print a log message for every row of <literal>pg_class</>. This
feature works similarly to other Tcl looping constructs; in
particular <literal>continue</> and <literal>break</> work in the
usual way inside the loop body.
will print a log message for every row of <literal>pg_class</>. This
feature works similarly to other Tcl looping constructs; in
particular <literal>continue</> and <literal>break</> work in the
usual way inside the loop body.
</para>
<para>
If a column of a query result is null, the target
variable for it is <quote>unset</> rather than being set.
variable for it is <quote>unset</> rather than being set.
</para>
</listitem>
</varlistentry>
@@ -304,27 +314,27 @@ spi_exec -array C "SELECT * FROM pg_class" {
<term><function>spi_prepare</function> <replaceable>query</replaceable> <replaceable>typelist</replaceable></term>
<listitem>
<para>
Prepares and saves a query plan for later execution. The
saved plan will be retained for the life of the current
session.<indexterm><primary>preparing a query</><secondary>in
PL/Tcl</></>
Prepares and saves a query plan for later execution. The
saved plan will be retained for the life of the current
session.<indexterm><primary>preparing a query</><secondary>in
PL/Tcl</></>
</para>
<para>
The query may use parameters, that is, placeholders for
values to be supplied whenever the plan is actually executed.
In the query string, refer to parameters
by the symbols <literal>$1</literal> ... <literal>$<replaceable>n</replaceable></literal>.
If the query uses parameters, the names of the parameter types
must be given as a Tcl list. (Write an empty list for
<replaceable>typelist</replaceable> if no parameters are used.)
Presently, the parameter types must be identified by the internal
type names shown in the system table <literal>pg_type</>; for example <literal>int4</> not
<literal>integer</>.
values to be supplied whenever the plan is actually executed.
In the query string, refer to parameters
by the symbols <literal>$1</literal> ... <literal>$<replaceable>n</replaceable></literal>.
If the query uses parameters, the names of the parameter types
must be given as a Tcl list. (Write an empty list for
<replaceable>typelist</replaceable> if no parameters are used.)
Presently, the parameter types must be identified by the internal
type names shown in the system table <literal>pg_type</>; for example <literal>int4</> not
<literal>integer</>.
</para>
<para>
The return value from <function>spi_prepare</function> is a query ID
to be used in subsequent calls to <function>spi_execp</function>. See
<function>spi_execp</function> for an example.
to be used in subsequent calls to <function>spi_execp</function>. See
<function>spi_execp</function> for an example.
</para>
</listitem>
</varlistentry>
@@ -333,31 +343,31 @@ spi_exec -array C "SELECT * FROM pg_class" {
<term><literal><function>spi_execp</> <optional role="tcl">-count <replaceable>n</replaceable></optional> <optional role="tcl">-array <replaceable>name</replaceable></optional> <optional role="tcl">-nulls <replaceable>string</replaceable></optional> <replaceable>queryid</replaceable> <optional role="tcl"><replaceable>value-list</replaceable></optional> <optional role="tcl"><replaceable>loop-body</replaceable></optional></literal></term>
<listitem>
<para>
Executes a query previously prepared with <function>spi_prepare</>.
<replaceable>queryid</replaceable> is the ID returned by
<function>spi_prepare</>. If the query references parameters,
a <replaceable>value-list</replaceable> must be supplied. This
is a Tcl list of actual values for the parameters. The list must be
the same length as the parameter type list previously given to
<function>spi_prepare</>. Omit <replaceable>value-list</replaceable>
if the query has no parameters.
Executes a query previously prepared with <function>spi_prepare</>.
<replaceable>queryid</replaceable> is the ID returned by
<function>spi_prepare</>. If the query references parameters,
a <replaceable>value-list</replaceable> must be supplied. This
is a Tcl list of actual values for the parameters. The list must be
the same length as the parameter type list previously given to
<function>spi_prepare</>. Omit <replaceable>value-list</replaceable>
if the query has no parameters.
</para>
<para>
The optional value for <literal>-nulls</> is a string of spaces and
<literal>'n'</> characters telling <function>spi_execp</function>
which of the parameters are null values. If given, it must have exactly the
same length as the <replaceable>value-list</replaceable>. If it
is not given, all the parameter values are nonnull.
The optional value for <literal>-nulls</> is a string of spaces and
<literal>'n'</> characters telling <function>spi_execp</function>
which of the parameters are null values. If given, it must have exactly the
same length as the <replaceable>value-list</replaceable>. If it
is not given, all the parameter values are nonnull.
</para>
<para>
Except for the way in which the query and its parameters are specified,
<function>spi_execp</> works just like <function>spi_exec</>.
<function>spi_execp</> works just like <function>spi_exec</>.
The <literal>-count</>, <literal>-array</>, and
<replaceable>loop-body</replaceable> options are the same,
and so is the result value.
<replaceable>loop-body</replaceable> options are the same,
and so is the result value.
</para>
<para>
Here's an example of a PL/Tcl function using a prepared plan:
Here's an example of a PL/Tcl function using a prepared plan:
<programlisting>
CREATE FUNCTION t1_count(integer, integer) RETURNS integer AS $$
@@ -389,9 +399,9 @@ $$ LANGUAGE pltcl;
<term><function>spi_lastoid</></term>
<listitem>
<para>
Returns the OID of the row inserted by the last
<function>spi_exec</> or <function>spi_execp</>,
if the command was a single-row <command>INSERT</>. (If not, you get zero.)
Returns the OID of the row inserted by the last
<function>spi_exec</> or <function>spi_execp</>,
if the command was a single-row <command>INSERT</>. (If not, you get zero.)
</para>
</listitem>
</varlistentry>
@@ -400,43 +410,43 @@ $$ LANGUAGE pltcl;
<term><function>quote</> <replaceable>string</replaceable></term>
<listitem>
<para>
Doubles all occurrences of single quote and backslash characters
in the given string. This may be used to safely quote strings
that are to be inserted into SQL commands given
to <function>spi_exec</function> or
<function>spi_prepare</function>.
For example, think about an SQL command string like
Doubles all occurrences of single quote and backslash characters
in the given string. This may be used to safely quote strings
that are to be inserted into SQL commands given
to <function>spi_exec</function> or
<function>spi_prepare</function>.
For example, think about an SQL command string like
<programlisting>
"SELECT '$val' AS ret"
</programlisting>
where the Tcl variable <literal>val</> actually contains
<literal>doesn't</literal>. This would result
in the final command string
where the Tcl variable <literal>val</> actually contains
<literal>doesn't</literal>. This would result
in the final command string
<programlisting>
SELECT 'doesn't' AS ret
</programlisting>
which would cause a parse error during
<function>spi_exec</function> or
<function>spi_prepare</function>.
To work properly, the submitted command should contain
which would cause a parse error during
<function>spi_exec</function> or
<function>spi_prepare</function>.
To work properly, the submitted command should contain
<programlisting>
SELECT 'doesn''t' AS ret
</programlisting>
which can be formed in PL/Tcl using
which can be formed in PL/Tcl using
<programlisting>
"SELECT '[ quote $val ]' AS ret"
</programlisting>
One advantage of <function>spi_execp</function> is that you don't
have to quote parameter values like this, since the parameters are never
parsed as part of an SQL command string.
have to quote parameter values like this, since the parameters are never
parsed as part of an SQL command string.
</para>
</listitem>
</varlistentry>
@@ -452,8 +462,7 @@ SELECT 'doesn''t' AS ret
Emits a log or error message. Possible levels are
<literal>DEBUG</>, <literal>LOG</>, <literal>INFO</>,
<literal>NOTICE</>, <literal>WARNING</>, <literal>ERROR</>, and
<literal>FATAL</>. Most simply emit the given message just like
the <literal>elog</> C function. <literal>ERROR</>
<literal>FATAL</>. <literal>ERROR</>
raises an error condition; if this is not trapped by the surrounding
Tcl code, the error propagates out to the calling query, causing
the current transaction or subtransaction to be aborted. This
@@ -461,7 +470,14 @@ SELECT 'doesn''t' AS ret
<literal>FATAL</> aborts the transaction and causes the current
session to shut down. (There is probably no good reason to use
this error level in PL/Tcl functions, but it's provided for
completeness.)
completeness.) The other levels only generate messages of different
priority levels.
Whether messages of a particular priority are reported to the client,
written to the server log, or both is controlled by the
<xref linkend="guc-log-min-messages"> and
<xref linkend="guc-client-min-messages"> configuration
variables. See <xref linkend="runtime-config"> for more
information.
</para>
</listitem>
</varlistentry>
@@ -494,100 +510,100 @@ SELECT 'doesn''t' AS ret
<varlistentry>
<term><varname>$TG_name</varname></term>
<listitem>
<para>
The name of the trigger from the <command>CREATE TRIGGER</command> statement.
</para>
<para>
The name of the trigger from the <command>CREATE TRIGGER</command> statement.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>$TG_relid</varname></term>
<listitem>
<para>
The object ID of the table that caused the trigger procedure
to be invoked.
</para>
<para>
The object ID of the table that caused the trigger procedure
to be invoked.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>$TG_relatts</varname></term>
<listitem>
<para>
A Tcl list of the table column names, prefixed with an empty list
<para>
A Tcl list of the table column names, prefixed with an empty list
element. So looking up a column name in the list with <application>Tcl</>'s
<function>lsearch</> command returns the element's number starting
with 1 for the first column, the same way the columns are customarily
numbered in <productname>PostgreSQL</productname>. (Empty list
elements also appear in the positions of columns that have been
dropped, so that the attribute numbering is correct for columns
to their right.)
</para>
with 1 for the first column, the same way the columns are customarily
numbered in <productname>PostgreSQL</productname>. (Empty list
elements also appear in the positions of columns that have been
dropped, so that the attribute numbering is correct for columns
to their right.)
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>$TG_when</varname></term>
<listitem>
<para>
The string <literal>BEFORE</> or <literal>AFTER</> depending on the
type of trigger call.
</para>
<para>
The string <literal>BEFORE</> or <literal>AFTER</> depending on the
type of trigger call.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>$TG_level</varname></term>
<listitem>
<para>
The string <literal>ROW</> or <literal>STATEMENT</> depending on the
type of trigger call.
</para>
<para>
The string <literal>ROW</> or <literal>STATEMENT</> depending on the
type of trigger call.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>$TG_op</varname></term>
<listitem>
<para>
The string <literal>INSERT</>, <literal>UPDATE</>, or
<literal>DELETE</> depending on the type of trigger call.
</para>
<para>
The string <literal>INSERT</>, <literal>UPDATE</>, or
<literal>DELETE</> depending on the type of trigger call.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>$NEW</varname></term>
<listitem>
<para>
An associative array containing the values of the new table
row for <command>INSERT</> or <command>UPDATE</> actions, or
empty for <command>DELETE</>. The array is indexed by column
name. Columns that are null will not appear in the array.
</para>
<para>
An associative array containing the values of the new table
row for <command>INSERT</> or <command>UPDATE</> actions, or
empty for <command>DELETE</>. The array is indexed by column
name. Columns that are null will not appear in the array.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>$OLD</varname></term>
<listitem>
<para>
An associative array containing the values of the old table
row for <command>UPDATE</> or <command>DELETE</> actions, or
empty for <command>INSERT</>. The array is indexed by column
name. Columns that are null will not appear in the array.
</para>
<para>
An associative array containing the values of the old table
row for <command>UPDATE</> or <command>DELETE</> actions, or
empty for <command>INSERT</>. The array is indexed by column
name. Columns that are null will not appear in the array.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>$args</varname></term>
<listitem>
<para>
A Tcl list of the arguments to the procedure as given in the
<command>CREATE TRIGGER</command> statement. These arguments are also accessible as
<literal>$1</literal> ... <literal>$<replaceable>n</replaceable></literal> in the procedure body.
</para>
<para>
A Tcl list of the arguments to the procedure as given in the
<command>CREATE TRIGGER</command> statement. These arguments are also accessible as
<literal>$1</literal> ... <literal>$<replaceable>n</replaceable></literal> in the procedure body.
</para>
</listitem>
</varlistentry>
@@ -644,39 +660,39 @@ CREATE TRIGGER trig_mytab_modcount BEFORE INSERT OR UPDATE ON mytab
<sect1 id="pltcl-unknown">
<title>Modules and the <function>unknown</> command</title>
<para>
PL/Tcl has support for autoloading Tcl code when used.
It recognizes a special table, <literal>pltcl_modules</>, which
is presumed to contain modules of Tcl code. If this table
exists, the module <literal>unknown</> is fetched from the table
and loaded into the Tcl interpreter immediately after creating
the interpreter.
PL/Tcl has support for autoloading Tcl code when used.
It recognizes a special table, <literal>pltcl_modules</>, which
is presumed to contain modules of Tcl code. If this table
exists, the module <literal>unknown</> is fetched from the table
and loaded into the Tcl interpreter immediately after creating
the interpreter.
</para>
<para>
While the <literal>unknown</> module could actually contain any
initialization script you need, it normally defines a Tcl
<function>unknown</> procedure that is invoked whenever Tcl does
not recognize an invoked procedure name. <application>PL/Tcl</>'s standard version
of this procedure tries to find a module in <literal>pltcl_modules</>
that will define the required procedure. If one is found, it is
loaded into the interpreter, and then execution is allowed to
proceed with the originally attempted procedure call. A
secondary table <literal>pltcl_modfuncs</> provides an index of
which functions are defined by which modules, so that the lookup
is reasonably quick.
initialization script you need, it normally defines a Tcl
<function>unknown</> procedure that is invoked whenever Tcl does
not recognize an invoked procedure name. <application>PL/Tcl</>'s standard version
of this procedure tries to find a module in <literal>pltcl_modules</>
that will define the required procedure. If one is found, it is
loaded into the interpreter, and then execution is allowed to
proceed with the originally attempted procedure call. A
secondary table <literal>pltcl_modfuncs</> provides an index of
which functions are defined by which modules, so that the lookup
is reasonably quick.
</para>
<para>
The <productname>PostgreSQL</productname> distribution includes
support scripts to maintain these tables:
<command>pltcl_loadmod</>, <command>pltcl_listmod</>,
<command>pltcl_delmod</>, as well as source for the standard
<literal>unknown</> module in <filename>share/unknown.pltcl</>. This module
must be loaded
into each database initially to support the autoloading mechanism.
support scripts to maintain these tables:
<command>pltcl_loadmod</>, <command>pltcl_listmod</>,
<command>pltcl_delmod</>, as well as source for the standard
<literal>unknown</> module in <filename>share/unknown.pltcl</>. This module
must be loaded
into each database initially to support the autoloading mechanism.
</para>
<para>
The tables <literal>pltcl_modules</> and <literal>pltcl_modfuncs</>
must be readable by all, but it is wise to make them owned and
writable only by the database administrator.
must be readable by all, but it is wise to make them owned and
writable only by the database administrator.
</para>
</sect1>