database/postgres
1
0
Fork 0
mirror of https://github.com/postgres/postgres.git synced 2025-07-02 09:02:37 +03:00
Code Activity

More editing of reference pages.

Browse Source
This commit is contained in:
Peter Eisentraut
2003-04-22 10:08:08 +00:00
parent 8a703496a2
commit 3450fd08a9
21 changed files with 2561 additions and 3612 deletions
Download Patch File Download Diff File Expand all files Collapse all files

256
doc/src/sgml/ref/create_function.sgml
View File

@ -1,5 +1,5 @@
<!--
$Header: /cvsroot/pgsql/doc/src/sgml/ref/create_function.sgml,v 1.46 2003/03/25 16:15:39 petere Exp $
$Header: /cvsroot/pgsql/doc/src/sgml/ref/create_function.sgml,v 1.47 2003/04/22 10:08:08 petere Exp $
-->
<refentry id="SQL-CREATEFUNCTION">
@ -38,25 +38,48 @@ CREATE [ OR REPLACE ] FUNCTION <replaceable class="parameter">name</replaceable>
</para>
<para>
The user that creates the function becomes the owner of the function.
If a schema name is included, then the function is created in the
specified schema. Otherwise it is created in the current schema.
The name of the new function must not match any existing function
with the same argument types in the same schema. However,
functions of different argument types may share a name (this is
called <firstterm>overloading</>).
</para>
<para>
To update the definition of an existing function, use
<command>CREATE OR REPLACE FUNCTION</command>. It is not possible
to change the name or argument types of a function this way (if you
tried, you'd just be creating a new, distinct function). Also,
<command>CREATE OR REPLACE FUNCTION</command> will not let you
change the return type of an existing function. To do that, you
must drop and recreate the function.
</para>
<para>
If you drop and then recreate a function, the new function is not
the same entity as the old; you will break existing rules, views,
triggers, etc. that referred to the old function. Use
<command>CREATE OR REPLACE FUNCTION</command> to change a function
definition without breaking objects that refer to the function.
</para>
<para>
The user that creates the function becomes the owner of the function.
</para>
</refsect1>
<refsect1>
<title>Parameters</title>
<variablelist>
<title>Parameters</title>
<varlistentry>
<term><replaceable class="parameter">name</replaceable></term>
<listitem>
<para>
The name of a function to create. If a schema name is included,
then the function is created in the
specified schema. Otherwise it is created in the current schema (the
one at the front of the search path; see <literal>CURRENT_SCHEMA()</>).
The name of the new function must not match any existing function
with the same argument types in the same schema. However, functions of
different argument types may share a name (this is called
<firstterm>overloading</>).
The name of a function to create.
</para>
</listitem>
</varlistentry>
@ -67,20 +90,21 @@ CREATE [ OR REPLACE ] FUNCTION <replaceable class="parameter">name</replaceable>
<listitem>
<para>
The data type(s) of the function's arguments (optionally
schema-qualified), if any. The input types may be base, complex, or
domain types, or the same as the type of an existing column.
schema-qualified), if any. The argument types may be base, complex, or
domain types, or copy the type of an existing column.
</para>
<para>
The type of a column is referenced by writing <replaceable
The type of a column is referenced by writing
<literal><replaceable
class="parameter">tablename</replaceable>.<replaceable
class="parameter">columnname</replaceable><literal>%TYPE</literal>;
class="parameter">columnname</replaceable>%TYPE</literal>;
using this can sometimes help make a function independent from
changes to the definition of a table.
</para>
<para>
Depending on the implementation language it may also be allowed
to specify <quote>pseudo-types</> such as <type>cstring</>.
Pseudo-types indicate that the actual argument type is either
to specify <quote>pseudotypes</> such as <type>cstring</>.
Pseudotypes indicate that the actual argument type is either
incompletely specified, or outside the set of ordinary SQL data types.
</para>
</listitem>
@ -92,15 +116,15 @@ CREATE [ OR REPLACE ] FUNCTION <replaceable class="parameter">name</replaceable>
<listitem>
<para>
The return data type (optionally schema-qualified). The return type
may be specified as a base, complex, domain type
or the same as the type of an existing column. See the description
may be specified as a base, complex, or domain type,
or may copy the type of an existing column. See the description
under <literal>argtype</literal> above on how to reference the type
of an existing column.
</para>
<para>
Depending on the implementation language it may also be allowed
to specify <quote>pseudo-types</> such as <type>cstring</>.
The <literal>setof</literal>
to specify <quote>pseudotypes</> such as <type>cstring</>.
The <literal>SETOF</literal>
modifier indicates that the function will return a set of
items, rather than a single item.
</para>
@ -123,9 +147,9 @@ CREATE [ OR REPLACE ] FUNCTION <replaceable class="parameter">name</replaceable>
</varlistentry>
<varlistentry>
<term>IMMUTABLE</term>
<term>STABLE</term>
<term>VOLATILE</term>
<term><literal>IMMUTABLE</literal></term>
<term><literal>STABLE</literal></term>
<term><literal>VOLATILE</literal></term>
<listitem>
<para>
@ -140,7 +164,7 @@ CREATE [ OR REPLACE ] FUNCTION <replaceable class="parameter">name</replaceable>
<literal>IMMUTABLE</literal> indicates that the function always
returns the same result when given the same argument values; that
is, it does not do database lookups or otherwise use information not
directly present in its parameter list. If this option is given,
directly present in its argument list. If this option is given,
any call of the function with all-constant arguments can be
immediately replaced with the function value.
</para>
@ -152,7 +176,7 @@ CREATE [ OR REPLACE ] FUNCTION <replaceable class="parameter">name</replaceable>
result could change across SQL statements. This is the appropriate
selection for functions whose results depend on database lookups,
parameter variables (such as the current time zone), etc. Also note
that the <literal>CURRENT_TIMESTAMP</> family of functions qualify
that the <function>current_timestamp</> family of functions qualify
as stable, since their values do not change within a transaction.
</para>
@ -170,9 +194,9 @@ CREATE [ OR REPLACE ] FUNCTION <replaceable class="parameter">name</replaceable>
</varlistentry>
<varlistentry>
<term>CALLED ON NULL INPUT</term>
<term>RETURNS NULL ON NULL INPUT</term>
<term>STRICT</term>
<term><literal>CALLED ON NULL INPUT</literal></term>
<term><literal>RETURNS NULL ON NULL INPUT</literal></term>
<term><literal>STRICT</literal></term>
<listitem>
<para>
@ -186,17 +210,17 @@ CREATE [ OR REPLACE ] FUNCTION <replaceable class="parameter">name</replaceable>
<para>
<literal>RETURNS NULL ON NULL INPUT</literal> or
<literal>STRICT</literal> indicates that the function always
returns NULL whenever any of its arguments are NULL. If this
returns null whenever any of its arguments are null. If this
parameter is specified, the function is not executed when there
are NULL arguments; instead a NULL result is assumed
are null arguments; instead a null result is assumed
automatically.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><optional>EXTERNAL</optional> SECURITY INVOKER</term>
<term><optional>EXTERNAL</optional> SECURITY DEFINER</term>
<term><literal><optional>EXTERNAL</optional> SECURITY INVOKER</literal></term>
<term><literal><optional>EXTERNAL</optional> SECURITY DEFINER</literal></term>
<listitem>
<para>
@ -209,7 +233,7 @@ CREATE [ OR REPLACE ] FUNCTION <replaceable class="parameter">name</replaceable>
<para>
The key word <literal>EXTERNAL</literal> is present for SQL
compatibility but is optional since, unlike in SQL, this feature
conformance but is optional since, unlike in SQL, this feature
does not only apply to external functions.
</para>
</listitem>
@ -222,25 +246,26 @@ CREATE [ OR REPLACE ] FUNCTION <replaceable class="parameter">name</replaceable>
<para>
A string defining the function; the meaning depends on the
language. It may be an internal function name, the path to an
object file, an SQL query, or text in a procedural language.
object file, an SQL command, or text in a procedural language.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="parameter">obj_file</replaceable>, <replaceable class="parameter">link_symbol</replaceable></term>
<term><literal><replaceable class="parameter">obj_file</replaceable>, <replaceable class="parameter">link_symbol</replaceable></literal></term>
<listitem>
<para>
This form of the <literal>AS</literal> clause is used for
dynamically linked C language functions when the function name
dynamically loadable C language functions when the function name
in the C language source code is not the same as the name of
the SQL function. The string <replaceable
class="parameter">obj_file</replaceable> is the name of the
file containing the dynamically loadable object, and
<replaceable class="parameter">link_symbol</replaceable> is the
object's link symbol, that is, the name of the function in the C
language source code.
function's link symbol, that is, the name of the function in the C
language source code. If the link symbol is omitted, it is assumed
to be the same as the name of the SQL function being defined.
</para>
</listitem>
</varlistentry>
@ -285,48 +310,47 @@ CREATE [ OR REPLACE ] FUNCTION <replaceable class="parameter">name</replaceable>
</refsect1>
<refsect1>
<title>Diagnostics</title>
<variablelist>
<varlistentry>
<term><computeroutput>CREATE FUNCTION</computeroutput></term>
<listitem>
<para>
Message returned if the function was successfully created.
</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1 id="sql-createfunction-notes">
<title>Notes</title>
<para>
Refer to <xref linkend="xfunc"> for further information on writing
external functions.
functions.
</para>
<para>
The full <acronym>SQL</acronym> type syntax is allowed for
input arguments and return value. However, some details of the
type specification (e.g., the precision field for
<type>numeric</type> types) are the responsibility of the
type <type>numeric</type>) are the responsibility of the
underlying function implementation and are silently swallowed
(i.e., not recognized or
enforced) by the <command>CREATE FUNCTION</command> command.
</para>
<para>
<productname>PostgreSQL</productname> allows function <firstterm>overloading</firstterm>;
that is, the same name can be used for several different functions
so long as they have distinct argument types. This facility must
be used with caution for internal and C-language functions, however.
</para>
<para>
Two <literal>internal</literal>
functions cannot have the same C name without causing
errors at link time. To get around that, give them different C names
(for example, use the argument types as part of the C names), then
specify those names in the AS clause of <command>CREATE FUNCTION</command>.
If the AS clause is left empty, then <command>CREATE FUNCTION</command>
assumes the C name of the function is the same as the SQL name.
</para>
<para>
Similarly, when overloading SQL function names with multiple C-language
functions, give
each C-language instance of the function a distinct name, then use
the alternative form of the <command>AS</command> clause in the
<command>CREATE FUNCTION</command> syntax to select the appropriate
C-language implementation of each overloaded SQL function.
<productname>PostgreSQL</productname> allows function
<firstterm>overloading</firstterm>; that is, the same name can be
used for several different functions so long as they have distinct
argument types. However, the C names of all functions must be
different, so you must give overloaded C functions different C
names (for example, use the argument types as part of the C
names).
</para>
<para>
@ -341,116 +365,26 @@ CREATE [ OR REPLACE ] FUNCTION <replaceable class="parameter">name</replaceable>
to remove user-defined functions.
</para>
<para>
To update the definition of an existing function, use
<command>CREATE OR REPLACE FUNCTION</command>. Note that it is
not possible to change the name or argument types of a function
this way (if you tried, you'd just be creating a new, distinct
function). Also, <command>CREATE OR REPLACE FUNCTION</command>
will not let you change the return type of an existing function.
To do that, you must drop and re-create the function.
</para>
<para>
If you drop and then re-create a function, the new function is not
the same entity as the old; you will break existing rules, views,
triggers, etc that referred to the old function. Use
<command>CREATE OR REPLACE FUNCTION</command> to change a function
definition without breaking objects that refer to the function.
</para>
<para>
To be able to define a function, the user must have the
<literal>USAGE</literal> privilege on the language.
</para>
<para>
By default, only the owner (creator) of the function has the right
to execute it. Other users must be granted the
<literal>EXECUTE</literal> privilege on the function to be able to
use it.
</para>
</refsect1>
<refsect1 id="sql-createfunction-examples">
<title>Examples</title>
<para>
To create a simple SQL function:
Here is a trivial example to help you get startet. For more
information and examples, see <xref linkend="xfunc">.
<programlisting>
CREATE FUNCTION one() RETURNS integer
AS 'SELECT 1 AS RESULT;'
LANGUAGE SQL;
SELECT one() AS answer;
<computeroutput>
answer
--------
1
</computeroutput>
CREATE FUNCTION add(integer, integer) RETURNS integer
AS 'select $1 + $2;'
LANGUAGE SQL
IMMUTABLE
RETURNS NULL ON NULL INPUT;
</programlisting>
</para>
<para>
The next example creates a C function by calling a routine from a
user-created shared library named <filename>funcs.so</> (the extension
may vary across platforms). The shared library file is sought in the
server's dynamic library search path. This particular routine calculates
a check digit and returns true if the check digit in the function
parameters is correct. It is intended for use in a CHECK
constraint.
<programlisting>
CREATE FUNCTION ean_checkdigit(char, char) RETURNS boolean
AS 'funcs' LANGUAGE C;
CREATE TABLE product (
id char(8) PRIMARY KEY,
eanprefix char(8) CHECK (eanprefix ~ '[0-9]{2}-[0-9]{5}')
REFERENCES brandname(ean_prefix),
eancode char(6) CHECK (eancode ~ '[0-9]{6}'),
CONSTRAINT ean CHECK (ean_checkdigit(eanprefix, eancode))
);
</programlisting>
</para>
<para>
The next example creates a function that does type conversion from the
user-defined type complex to the built-in type point. The
function is implemented by a dynamically loaded object that was
compiled from C source (we illustrate the now-deprecated alternative
of specifying the absolute file name to the shared object file).
For <productname>PostgreSQL</productname> to
find a type conversion function automatically, the SQL function has
to have the same name as the return type, and so overloading is
unavoidable. The function name is overloaded by using the second
form of the <command>AS</command> clause in the SQL definition:
<programlisting>
CREATE FUNCTION point(complex) RETURNS point
AS '/home/bernie/pgsql/lib/complex.so', 'complex_to_point'
LANGUAGE C STRICT;
</programlisting>
The C declaration of the function could be:
<programlisting>
Point * complex_to_point (Complex *z)
{
Point *p;
p = (Point *) palloc(sizeof(Point));
p->x = z->x;
p->y = z->y;
return p;
}
</programlisting>
Note that the function is marked <quote>strict</>; this allows us
to skip checking for NULL input in the function body.
</para>
</refsect1>