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$Header: /cvsroot/pgsql/doc/src/sgml/ref/create_function.sgml,v 1.23 2001/05/19 09:01:10 petere Exp $
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<refentry id="SQL-CREATEFUNCTION">
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<refmeta>
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<refentrytitle>CREATE FUNCTION</refentrytitle>
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<refmiscinfo>SQL - Language Statements</refmiscinfo>
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</refmeta>
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<refnamediv>
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<refname>CREATE FUNCTION</refname>
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<refpurpose>Defines a new function</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<synopsis>
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CREATE FUNCTION <replaceable class="parameter">name</replaceable> ( [ <replaceable class="parameter">argtype</replaceable> [, ...] ] )
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RETURNS <replaceable class="parameter">rettype</replaceable>
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AS '<replaceable class="parameter">definition</replaceable>'
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LANGUAGE '<replaceable class="parameter">langname</replaceable>'
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[ WITH ( <replaceable class="parameter">attribute</replaceable> [, ...] ) ]
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CREATE FUNCTION <replaceable class="parameter">name</replaceable> ( [ <replaceable class="parameter">argtype</replaceable> [, ...] ] )
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RETURNS <replaceable class="parameter">rettype</replaceable>
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AS '<replaceable class="parameter">obj_file</replaceable>', '<replaceable class="parameter">link_symbol</replaceable>'
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LANGUAGE '<replaceable class="parameter">langname</replaceable>'
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[ WITH ( <replaceable class="parameter">attribute</replaceable> [, ...] ) ]
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</synopsis>
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</refsynopsisdiv>
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<refsect1 id="sql-createfunction-description">
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<title>Description</title>
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<para>
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<command>CREATE FUNCTION</command> defines a new function.
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<variablelist>
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<title>Parameters</title>
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<varlistentry>
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<term><replaceable class="parameter">name</replaceable></term>
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<listitem>
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<para>
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The name of a function to create. The name need not be unique,
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because functions may be overloaded, but functions with the
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same name must have different argument types.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><replaceable class="parameter">argtype</replaceable></term>
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<listitem>
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<para>
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The data type(s) of the function's arguments, if any. The
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input types may be base or complex types, or
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<literal>opaque</literal>. <literal>Opaque</literal> indicates
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that the function accepts arguments of a non-SQL type such as
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<type>char *</type>.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><replaceable class="parameter">rettype</replaceable></term>
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<listitem>
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<para>
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The return data type. The output type may be specified as a
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base type, complex type, <literal>setof</literal> type, or
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<literal>opaque</literal>. The <literal>setof</literal>
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modifier indicates that the function will return a set of
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items, rather than a single item. Functions with a declared
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return type of <literal>opaque</literal> do not return a value.
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These cannot be called directly; trigger functions make use of
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this feature.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><replaceable class="parameter">definition</replaceable></term>
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<listitem>
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<para>
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A string defining the function; the meaning depends on the
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language. It may be an internal function name, the path to an
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object file, an SQL query, or text in a procedural language.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><replaceable class="parameter">obj_file</replaceable>, <replaceable class="parameter">link_symbol</replaceable></term>
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<listitem>
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<para>
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This form of the <literal>AS</literal> clause is used for
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dynamically linked C language functions when the function name
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in the C language source code is not the same as the name of
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the SQL function. The string <replaceable
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class="parameter">obj_file</replaceable> is the name of the
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file containing the dynamically loadable object, and
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<replaceable class="parameter">link_symbol</replaceable> is the
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object's link symbol, that is, the name of the function in the C
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language source code.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><replaceable class="parameter">langname</replaceable></term>
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<listitem>
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<para>
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May be '<literal>sql</literal>', '<literal>C</literal>',
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'<literal>internal</literal>', or '<replaceable
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class="parameter">plname</replaceable>', where '<replaceable
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class="parameter">plname</replaceable>' is the name of a
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created procedural language. See
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<xref linkend="sql-createlanguage">
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for details.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><replaceable class="parameter">attribute</replaceable></term>
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<listitem>
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<para>
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An optional piece of information about the function, used for
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optimization. See below for details.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</para>
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<para>
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The user that creates the function becomes the owner of the function.
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</para>
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<para>
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The following attributes may appear in the WITH clause:
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<variablelist>
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<varlistentry>
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<term>iscachable</term>
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<listitem>
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<para>
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<option>Iscachable</option> indicates that the function always
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returns the same result when given the same argument values (i.e.,
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it does not do database lookups or otherwise use information not
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directly present in its parameter list). The optimizer uses
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<option>iscachable</option> to know whether it is safe to
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pre-evaluate a call of the function.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>isstrict</term>
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<listitem>
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<para>
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<option>isstrict</option> indicates that the function always
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returns NULL whenever any of its arguments are NULL. If this
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attribute is specified, the function is not executed when there
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are NULL arguments; instead a NULL result is assumed automatically.
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When <option>isstrict</option> is not specified, the function will
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be called for NULL inputs. It is then the function author's
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responsibility to check for NULLs if necessary and respond
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appropriately.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</para>
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2001-05-19 11:01:10 +02:00
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</refsect1>
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2001-05-19 11:01:10 +02:00
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<refsect1 id="sql-createfunction-notes">
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<title>Notes</title>
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2000-03-27 19:14:43 +02:00
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1999-06-14 09:37:05 +02:00
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<para>
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2000-03-27 19:14:43 +02:00
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Refer to the chapter in the
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<citetitle>PostgreSQL Programmer's Guide</citetitle>
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on the topic of extending
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<productname>Postgres</productname> via functions
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for further information on writing external functions.
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</para>
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1999-06-14 09:37:05 +02:00
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<para>
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1998-09-16 16:43:12 +02:00
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Use <command>DROP FUNCTION</command>
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to remove user-defined functions.
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</para>
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1999-05-20 04:57:15 +02:00
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2000-03-27 19:14:43 +02:00
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<para>
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2001-05-19 11:01:10 +02:00
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The full <acronym>SQL</acronym> type syntax is allowed for
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input arguments and return value. However, some details of the
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2000-10-05 21:48:34 +02:00
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type specification (e.g., the precision field for
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<type>numeric</type> types) are the responsibility of the
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underlying function implementation and are silently swallowed
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(i.e., not recognized or
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enforced) by the <command>CREATE FUNCTION</command> command.
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</para>
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1999-05-20 04:57:15 +02:00
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1999-07-22 17:09:15 +02:00
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<para>
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<productname>Postgres</productname> allows function <firstterm>overloading</firstterm>;
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that is, the same name can be used for several different functions
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so long as they have distinct argument types. This facility must
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be used with caution for internal and C-language functions, however.
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</para>
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<para>
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2000-11-20 21:36:57 +01:00
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Two <literal>internal</literal>
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functions cannot have the same C name without causing
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errors at link time. To get around that, give them different C names
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(for example, use the argument types as part of the C names), then
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specify those names in the AS clause of <command>CREATE FUNCTION</command>.
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2000-10-05 21:48:34 +02:00
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If the AS clause is left empty, then <command>CREATE FUNCTION</command>
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assumes the C name of the function is the same as the SQL name.
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</para>
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1999-05-20 04:57:15 +02:00
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1999-07-22 17:09:15 +02:00
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<para>
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2000-08-25 01:36:29 +02:00
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Similarly, when overloading SQL function names with multiple C-language
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functions, give
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each C-language instance of the function a distinct name, then use
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I have been working with user defined types and user defined c
functions. One problem that I have encountered with the function
manager is that it does not allow the user to define type conversion
functions that convert between user types. For instance if mytype1,
mytype2, and mytype3 are three Postgresql user types, and if I wish to
define Postgresql conversion functions like
I run into problems, because the Postgresql dynamic loader would look
for a single link symbol, mytype3, for both pieces of object code. If
I just change the name of one of the Postgresql functions (to make the
symbols distinct), the automatic type conversion that Postgresql uses,
for example, when matching operators to arguments no longer finds the
type conversion function.
The solution that I propose, and have implemented in the attatched
patch extends the CREATE FUNCTION syntax as follows. In the first case
above I use the link symbol mytype2_to_mytype3 for the link object
that implements the first conversion function, and define the
Postgresql operator with the following syntax
The patch includes changes to the parser to include the altered
syntax, changes to the ProcedureStmt node in nodes/parsenodes.h,
changes to commands/define.c to handle the extra information in the AS
clause, and changes to utils/fmgr/dfmgr.c that alter the way that the
dynamic loader figures out what link symbol to use. I store the
string for the link symbol in the prosrc text attribute of the pg_proc
table which is currently unused in rows that reference dynamically
loaded
functions.
Bernie Frankpitt
1999-09-28 06:34:56 +02:00
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the alternative form of the <command>AS</command> clause in the
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2000-08-25 01:36:29 +02:00
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<command>CREATE FUNCTION</command> syntax to select the appropriate
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C-language implementation of each overloaded SQL function.
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1999-07-22 17:09:15 +02:00
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</para>
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2001-05-19 11:01:10 +02:00
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<para>
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When repeated <command>CREATE FUNCTION</command> calls refer to
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the same object file, the file is only loaded once. To unload and
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reload the file (perhaps during development), use the <xref
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linkend="sql-load"> command.
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</para>
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|
1998-12-29 03:24:47 +01:00
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</refsect1>
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2001-05-19 11:01:10 +02:00
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1998-05-13 07:34:00 +02:00
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2001-05-19 11:01:10 +02:00
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<refsect1 id="sql-createfunction-examples">
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<title>Examples</title>
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1999-06-14 09:37:05 +02:00
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<para>
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1998-05-13 07:34:00 +02:00
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To create a simple SQL function:
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1999-07-06 19:16:42 +02:00
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2001-05-19 11:01:10 +02:00
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<programlisting>
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CREATE FUNCTION one() RETURNS integer
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AS 'SELECT 1 AS RESULT;'
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1999-07-06 19:16:42 +02:00
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LANGUAGE 'sql';
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2001-05-19 11:01:10 +02:00
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SELECT one() AS answer;
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<computeroutput>
|
2000-03-26 20:32:30 +02:00
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answer
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--------
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1
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2001-05-19 11:01:10 +02:00
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</computeroutput>
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</programlisting>
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1999-07-06 19:16:42 +02:00
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</para>
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|
1998-05-13 07:34:00 +02:00
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<para>
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2001-05-19 11:01:10 +02:00
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The next example creates a C function by calling a routine from a
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user-created shared library. This particular routine calculates a
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check digit and returns TRUE if the check digit in the function
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parameters is correct. It is intended for use in a CHECK
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constraint.
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<programlisting>
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CREATE FUNCTION ean_checkdigit(char, char) RETURNS boolean
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1999-07-06 19:16:42 +02:00
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AS '/usr1/proj/bray/sql/funcs.so' LANGUAGE 'c';
|
1998-12-29 03:24:47 +01:00
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1999-07-06 19:16:42 +02:00
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CREATE TABLE product (
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1999-06-14 09:37:05 +02:00
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id char(8) PRIMARY KEY,
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eanprefix char(8) CHECK (eanprefix ~ '[0-9]{2}-[0-9]{5}')
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|
REFERENCES brandname(ean_prefix),
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eancode char(6) CHECK (eancode ~ '[0-9]{6}'),
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|
|
CONSTRAINT ean CHECK (ean_checkdigit(eanprefix, eancode))
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1999-07-06 19:16:42 +02:00
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);
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2001-05-19 11:01:10 +02:00
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|
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</programlisting>
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</para>
|
I have been working with user defined types and user defined c
functions. One problem that I have encountered with the function
manager is that it does not allow the user to define type conversion
functions that convert between user types. For instance if mytype1,
mytype2, and mytype3 are three Postgresql user types, and if I wish to
define Postgresql conversion functions like
I run into problems, because the Postgresql dynamic loader would look
for a single link symbol, mytype3, for both pieces of object code. If
I just change the name of one of the Postgresql functions (to make the
symbols distinct), the automatic type conversion that Postgresql uses,
for example, when matching operators to arguments no longer finds the
type conversion function.
The solution that I propose, and have implemented in the attatched
patch extends the CREATE FUNCTION syntax as follows. In the first case
above I use the link symbol mytype2_to_mytype3 for the link object
that implements the first conversion function, and define the
Postgresql operator with the following syntax
The patch includes changes to the parser to include the altered
syntax, changes to the ProcedureStmt node in nodes/parsenodes.h,
changes to commands/define.c to handle the extra information in the AS
clause, and changes to utils/fmgr/dfmgr.c that alter the way that the
dynamic loader figures out what link symbol to use. I store the
string for the link symbol in the prosrc text attribute of the pg_proc
table which is currently unused in rows that reference dynamically
loaded
functions.
Bernie Frankpitt
1999-09-28 06:34:56 +02:00
|
|
|
|
|
|
|
<para>
|
|
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|
This example creates a function that does type conversion between the
|
2000-10-05 21:48:34 +02:00
|
|
|
user-defined type complex, and the internal type point. The
|
I have been working with user defined types and user defined c
functions. One problem that I have encountered with the function
manager is that it does not allow the user to define type conversion
functions that convert between user types. For instance if mytype1,
mytype2, and mytype3 are three Postgresql user types, and if I wish to
define Postgresql conversion functions like
I run into problems, because the Postgresql dynamic loader would look
for a single link symbol, mytype3, for both pieces of object code. If
I just change the name of one of the Postgresql functions (to make the
symbols distinct), the automatic type conversion that Postgresql uses,
for example, when matching operators to arguments no longer finds the
type conversion function.
The solution that I propose, and have implemented in the attatched
patch extends the CREATE FUNCTION syntax as follows. In the first case
above I use the link symbol mytype2_to_mytype3 for the link object
that implements the first conversion function, and define the
Postgresql operator with the following syntax
The patch includes changes to the parser to include the altered
syntax, changes to the ProcedureStmt node in nodes/parsenodes.h,
changes to commands/define.c to handle the extra information in the AS
clause, and changes to utils/fmgr/dfmgr.c that alter the way that the
dynamic loader figures out what link symbol to use. I store the
string for the link symbol in the prosrc text attribute of the pg_proc
table which is currently unused in rows that reference dynamically
loaded
functions.
Bernie Frankpitt
1999-09-28 06:34:56 +02:00
|
|
|
function is implemented by a dynamically loaded object that was
|
2001-05-19 11:01:10 +02:00
|
|
|
compiled from C source. For <productname>PostgreSQL</productname> to
|
|
|
|
find a type conversion function automatically, the SQL function has
|
2000-08-25 01:36:29 +02:00
|
|
|
to have the same name as the return type, and so overloading is
|
I have been working with user defined types and user defined c
functions. One problem that I have encountered with the function
manager is that it does not allow the user to define type conversion
functions that convert between user types. For instance if mytype1,
mytype2, and mytype3 are three Postgresql user types, and if I wish to
define Postgresql conversion functions like
I run into problems, because the Postgresql dynamic loader would look
for a single link symbol, mytype3, for both pieces of object code. If
I just change the name of one of the Postgresql functions (to make the
symbols distinct), the automatic type conversion that Postgresql uses,
for example, when matching operators to arguments no longer finds the
type conversion function.
The solution that I propose, and have implemented in the attatched
patch extends the CREATE FUNCTION syntax as follows. In the first case
above I use the link symbol mytype2_to_mytype3 for the link object
that implements the first conversion function, and define the
Postgresql operator with the following syntax
The patch includes changes to the parser to include the altered
syntax, changes to the ProcedureStmt node in nodes/parsenodes.h,
changes to commands/define.c to handle the extra information in the AS
clause, and changes to utils/fmgr/dfmgr.c that alter the way that the
dynamic loader figures out what link symbol to use. I store the
string for the link symbol in the prosrc text attribute of the pg_proc
table which is currently unused in rows that reference dynamically
loaded
functions.
Bernie Frankpitt
1999-09-28 06:34:56 +02:00
|
|
|
unavoidable. The function name is overloaded by using the second
|
2000-07-22 04:39:10 +02:00
|
|
|
form of the <command>AS</command> clause in the SQL definition:
|
2001-05-19 11:01:10 +02:00
|
|
|
|
|
|
|
<programlisting>
|
I have been working with user defined types and user defined c
functions. One problem that I have encountered with the function
manager is that it does not allow the user to define type conversion
functions that convert between user types. For instance if mytype1,
mytype2, and mytype3 are three Postgresql user types, and if I wish to
define Postgresql conversion functions like
I run into problems, because the Postgresql dynamic loader would look
for a single link symbol, mytype3, for both pieces of object code. If
I just change the name of one of the Postgresql functions (to make the
symbols distinct), the automatic type conversion that Postgresql uses,
for example, when matching operators to arguments no longer finds the
type conversion function.
The solution that I propose, and have implemented in the attatched
patch extends the CREATE FUNCTION syntax as follows. In the first case
above I use the link symbol mytype2_to_mytype3 for the link object
that implements the first conversion function, and define the
Postgresql operator with the following syntax
The patch includes changes to the parser to include the altered
syntax, changes to the ProcedureStmt node in nodes/parsenodes.h,
changes to commands/define.c to handle the extra information in the AS
clause, and changes to utils/fmgr/dfmgr.c that alter the way that the
dynamic loader figures out what link symbol to use. I store the
string for the link symbol in the prosrc text attribute of the pg_proc
table which is currently unused in rows that reference dynamically
loaded
functions.
Bernie Frankpitt
1999-09-28 06:34:56 +02:00
|
|
|
CREATE FUNCTION point(complex) RETURNS point
|
|
|
|
AS '/home/bernie/pgsql/lib/complex.so', 'complex_to_point'
|
|
|
|
LANGUAGE 'c';
|
2001-05-19 11:01:10 +02:00
|
|
|
</programlisting>
|
|
|
|
|
|
|
|
The C declaration of the function could be:
|
|
|
|
|
|
|
|
<programlisting>
|
I have been working with user defined types and user defined c
functions. One problem that I have encountered with the function
manager is that it does not allow the user to define type conversion
functions that convert between user types. For instance if mytype1,
mytype2, and mytype3 are three Postgresql user types, and if I wish to
define Postgresql conversion functions like
I run into problems, because the Postgresql dynamic loader would look
for a single link symbol, mytype3, for both pieces of object code. If
I just change the name of one of the Postgresql functions (to make the
symbols distinct), the automatic type conversion that Postgresql uses,
for example, when matching operators to arguments no longer finds the
type conversion function.
The solution that I propose, and have implemented in the attatched
patch extends the CREATE FUNCTION syntax as follows. In the first case
above I use the link symbol mytype2_to_mytype3 for the link object
that implements the first conversion function, and define the
Postgresql operator with the following syntax
The patch includes changes to the parser to include the altered
syntax, changes to the ProcedureStmt node in nodes/parsenodes.h,
changes to commands/define.c to handle the extra information in the AS
clause, and changes to utils/fmgr/dfmgr.c that alter the way that the
dynamic loader figures out what link symbol to use. I store the
string for the link symbol in the prosrc text attribute of the pg_proc
table which is currently unused in rows that reference dynamically
loaded
functions.
Bernie Frankpitt
1999-09-28 06:34:56 +02:00
|
|
|
Point * complex_to_point (Complex *z)
|
|
|
|
{
|
|
|
|
Point *p;
|
|
|
|
|
|
|
|
p = (Point *) palloc(sizeof(Point));
|
|
|
|
p->x = z->x;
|
|
|
|
p->y = z->y;
|
|
|
|
|
|
|
|
return p;
|
|
|
|
}
|
2001-05-19 11:01:10 +02:00
|
|
|
</programlisting>
|
|
|
|
</para>
|
1999-06-14 09:37:05 +02:00
|
|
|
</refsect1>
|
2001-05-19 11:01:10 +02:00
|
|
|
|
1998-05-13 07:34:00 +02:00
|
|
|
|
2001-05-19 11:01:10 +02:00
|
|
|
<refsect1 id="sql-createfunction-compat">
|
|
|
|
<title>Compatibility</title>
|
1999-07-22 17:09:15 +02:00
|
|
|
|
2001-05-19 11:01:10 +02:00
|
|
|
<para>
|
|
|
|
A <command>CREATE FUNCTION</command> command is defined in SQL99.
|
|
|
|
The <application>PostgreSQL</application> version is similar but
|
|
|
|
not compatible. The attributes are not portable, neither are the
|
|
|
|
different available languages.
|
|
|
|
</para>
|
|
|
|
</refsect1>
|
1998-09-16 16:43:12 +02:00
|
|
|
|
2001-05-19 11:01:10 +02:00
|
|
|
|
|
|
|
<refsect1 id="sql-createfunction-seealso">
|
|
|
|
<title>See Also</title>
|
|
|
|
|
|
|
|
<para>
|
|
|
|
<xref linkend="sql-dropfunction">,
|
|
|
|
<xref linkend="sql-load">,
|
|
|
|
<citetitle>PostgreSQL Programmer's Guide</citetitle>
|
|
|
|
</para>
|
1998-05-13 07:34:00 +02:00
|
|
|
</refsect1>
|
2001-05-19 11:01:10 +02:00
|
|
|
|
1999-06-14 09:37:05 +02:00
|
|
|
</refentry>
|
1998-05-13 07:34:00 +02:00
|
|
|
|
|
|
|
<!-- Keep this comment at the end of the file
|
|
|
|
Local variables:
|
2000-03-27 19:14:43 +02:00
|
|
|
mode:sgml
|
1999-06-14 09:37:05 +02:00
|
|
|
sgml-omittag:nil
|
1998-05-13 07:34:00 +02:00
|
|
|
sgml-shorttag:t
|
|
|
|
sgml-minimize-attributes:nil
|
|
|
|
sgml-always-quote-attributes:t
|
|
|
|
sgml-indent-step:1
|
|
|
|
sgml-indent-data:t
|
|
|
|
sgml-parent-document:nil
|
|
|
|
sgml-default-dtd-file:"../reference.ced"
|
|
|
|
sgml-exposed-tags:nil
|
2000-03-27 19:14:43 +02:00
|
|
|
sgml-local-catalogs:("/usr/lib/sgml/catalog")
|
1998-05-13 07:34:00 +02:00
|
|
|
sgml-local-ecat-files:nil
|
|
|
|
End:
|
|
|
|
-->
|