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$Header: /cvsroot/pgsql/doc/src/sgml/ref/create_function.sgml,v 1.11 1999/10/02 21:27:49 tgl Exp $

Postgres documentation

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</refnamediv>

<refsynopsisdiv>

<refsynopsisdivinfo>

<date>1999-07-20</date>

<date>1999-10-02</date>

</refsynopsisdivinfo>

<synopsis>

CREATE FUNCTION <replaceable class="parameter">name</replaceable> ( [ <replaceable class="parameter">ftype</replaceable> [, ...] ] )

RETURNS <replaceable class="parameter">rtype</replaceable>

[ WITH ( <replaceable class="parameter">attribute</replaceable> [, ...] ) ]

AS <replaceable class="parameter">definition</replaceable>

LANGUAGE '<replaceable class="parameter">langname</replaceable>'

CREATE FUNCTION <replaceable class="parameter">name</replaceable> ( [ <replaceable class="parameter">ftype</replaceable> [, ...] ] )

RETURNS <replaceable class="parameter">rtype</replaceable>

[ WITH ( <replaceable class="parameter">attribute</replaceable> [, ...] ) ]

AS <replaceable class="parameter">obj_file</replaceable> , <replaceable class="parameter">link_symbol</replaceable>

LANGUAGE 'c'

LANGUAGE 'C'

</synopsis>

<refsect2 id="R2-SQL-CREATEFUNCTION-1">

</para>

</listitem>

</varlistentry>

<varlistentry>

<term><replaceable class="parameter">attribute</replaceable></term>

<listitem>

<para>

An optional piece of information about the function, used for

optimization. The only attribute currently supported is

<literal>iscachable</literal>.

<literal>iscachable</literal> indicates that the function always

returns the same result when given the same input values (i.e.,

it does not do database lookups or otherwise use information not

directly present in its parameter list). The optimizer uses

<literal>iscachable</literal> to know whether it is safe to

pre-evaluate a call of the function.

</para>

</listitem>

</varlistentry>

<varlistentry>

<term><replaceable class="parameter">definition</replaceable></term>

<listitem>

'<literal>internal</literal>'

or '<replaceable class="parameter">plname</replaceable>',

where '<replaceable class="parameter">plname</replaceable>'

is the name of a created procedural

language. See

is the name of a created procedural language. See

<xref linkend="sql-createlanguage-title" endterm="sql-createlanguage-title">

for details.

</para>

has the same name as the C source function the first form of the

statement is used. The string argument in the AS clause is the

full pathname of the file that contains the dynamically loadable

compiled object. If the name of C function is different from the

name of the SQL function, then the second form is used. In this

compiled object. If the name oftheC function is different from the

desiredname of the SQL function, then the second form is used. In this

form the AS clause takes two string arguments, the first is the

full pathname of the dynamically loadable object file, and the

second is the link symbol that the dynamic loader should search

code file for the function, bracketed by quotation marks. If a

link symbol is used in the AS clause, the link symbol should also be

bracketed by single quotation marks, and should be exactly the

same as the name of function in the C source code. On UNIX systems

same as the name ofthefunction in the C source code. On UNIX systems

the command <command>nm</command> will print all of the link

symbols in a dynamically loadable object.

(<productname>Postgres</productname> will not compile a function

</para>

<sect3>

<title>Pre-v6.5</title>

<title>Pre-v6.6</title>

<para>

For functions written in C, the SQL name declared in

they can be declared with the same SQL names (as long as their

argument types differ, of course). This way avoids the overhead of

an SQL wrapper function, at the cost of more effort to prepare a

custom backend executable.

custom backend executable. (This option is only available in version

6.5 and later, since prior versions required internal functions to

have the same name in SQL as in the C code.)

</para>

</sect3>

</sect2>