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><H1
><A
NAME="SQL-CREATELANGUAGE"
></A
>CREATE LANGUAGE</H1
><DIV
CLASS="REFNAMEDIV"
><A
NAME="AEN52743"
></A
><H2
>Name</H2
>CREATE LANGUAGE -- define a new procedural language</DIV
><A
NAME="AEN52746"
></A
><DIV
CLASS="REFSYNOPSISDIV"
><A
NAME="AEN52748"
></A
><H2
>Synopsis</H2
><PRE
CLASS="SYNOPSIS"
>CREATE [ PROCEDURAL ] LANGUAGE <TT
CLASS="REPLACEABLE"
><I
>name</I
></TT
>
CREATE [ TRUSTED ] [ PROCEDURAL ] LANGUAGE <TT
CLASS="REPLACEABLE"
><I
>name</I
></TT
>
HANDLER <TT
CLASS="REPLACEABLE"
><I
>call_handler</I
></TT
> [ VALIDATOR <TT
CLASS="REPLACEABLE"
><I
>valfunction</I
></TT
> ]</PRE
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="SQL-CREATELANGUAGE-DESCRIPTION"
></A
><H2
>Description</H2
><P
> Using <TT
CLASS="COMMAND"
>CREATE LANGUAGE</TT
>, a
<SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> user can register a new
procedural language with a <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
>
database. Subsequently, functions and trigger procedures can be
defined in this new language.
</P
><P
> <TT
CLASS="COMMAND"
>CREATE LANGUAGE</TT
> effectively associates the
language name with a call handler that is responsible for executing
functions written in the language. Refer to <A
HREF="xplang.html"
>Chapter 37</A
>
for more information about language call handlers.
</P
><P
> There are two forms of the <TT
CLASS="COMMAND"
>CREATE LANGUAGE</TT
> command.
In the first form, the user supplies just the name of the desired
language, and the <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> server consults
the <A
HREF="catalog-pg-pltemplate.html"
><TT
CLASS="STRUCTNAME"
>pg_pltemplate</TT
></A
>
system catalog to determine the correct parameters. In the second form,
the user supplies the language parameters along with the language name.
The second form can be used to create a language that is not defined in
<TT
CLASS="STRUCTNAME"
>pg_pltemplate</TT
>, but this approach is considered obsolescent.
</P
><P
> When the server finds an entry in the <TT
CLASS="STRUCTNAME"
>pg_pltemplate</TT
> catalog
for the given language name, it will use the catalog data even if the
command includes language parameters. This behavior simplifies loading of
old dump files, which are likely to contain out-of-date information
about language support functions.
</P
><P
> Ordinarily, the user must have the
<SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> superuser privilege to
register a new language. However, the owner of a database can register
a new language within that database if the language is listed in
the <TT
CLASS="STRUCTNAME"
>pg_pltemplate</TT
> catalog and is marked
as allowed to be created by database owners (<TT
CLASS="STRUCTFIELD"
>tmpldbacreate</TT
>
is true). The default is that trusted languages can be created
by database owners, but this can be adjusted by superusers by modifying
the contents of <TT
CLASS="STRUCTNAME"
>pg_pltemplate</TT
>.
The creator of a language becomes its owner and can later
drop it, rename it, or assign it to a new owner.
</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="SQL-CREATELANGUAGE-PARAMETERS"
></A
><H2
>Parameters</H2
><P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><TT
CLASS="LITERAL"
>TRUSTED</TT
></DT
><DD
><P
> <TT
CLASS="LITERAL"
>TRUSTED</TT
> specifies that the call handler for
the language is safe, that is, it does not offer an
unprivileged user any functionality to bypass access
restrictions. If this key word is omitted when registering the
language, only users with the
<SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> superuser privilege can
use this language to create new functions.
</P
></DD
><DT
><TT
CLASS="LITERAL"
>PROCEDURAL</TT
></DT
><DD
><P
> This is a noise word.
</P
></DD
><DT
><TT
CLASS="REPLACEABLE"
><I
>name</I
></TT
></DT
><DD
><P
> The name of the new procedural language. The language name is
case insensitive. The name must be unique among the languages
in the database.
</P
><P
> For backward compatibility, the name can be enclosed by single
quotes.
</P
></DD
><DT
><TT
CLASS="LITERAL"
>HANDLER</TT
> <TT
CLASS="REPLACEABLE"
><I
>call_handler</I
></TT
></DT
><DD
><P
> <TT
CLASS="REPLACEABLE"
><I
>call_handler</I
></TT
> is
the name of a previously registered function that will be
called to execute the procedural language functions. The call
handler for a procedural language must be written in a compiled
language such as C with version 1 call convention and
registered with <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> as a
function taking no arguments and returning the
<TT
CLASS="TYPE"
>language_handler</TT
> type, a placeholder type that is
simply used to identify the function as a call handler.
</P
></DD
><DT
><TT
CLASS="LITERAL"
>VALIDATOR</TT
> <TT
CLASS="REPLACEABLE"
><I
>valfunction</I
></TT
></DT
><DD
><P
> <TT
CLASS="REPLACEABLE"
><I
>valfunction</I
></TT
> is the
name of a previously registered function that will be called
when a new function in the language is created, to validate the
new function.
If no
validator function is specified, then a new function will not
be checked when it is created.
The validator function must take one argument of
type <TT
CLASS="TYPE"
>oid</TT
>, which will be the OID of the
to-be-created function, and will typically return <TT
CLASS="TYPE"
>void</TT
>.
</P
><P
> A validator function would typically inspect the function body
for syntactical correctness, but it can also look at other
properties of the function, for example if the language cannot
handle certain argument types. To signal an error, the
validator function should use the <CODE
CLASS="FUNCTION"
>ereport()</CODE
>
function. The return value of the function is ignored.
</P
></DD
></DL
></DIV
><P
> The <TT
CLASS="LITERAL"
>TRUSTED</TT
> option and the support function name(s) are
ignored if the server has an entry for the specified language
name in <TT
CLASS="STRUCTNAME"
>pg_pltemplate</TT
>.
</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="SQL-CREATELANGUAGE-NOTES"
></A
><H2
>Notes</H2
><P
> The <A
HREF="app-createlang.html"
><SPAN
CLASS="APPLICATION"
>createlang</SPAN
></A
> program is a simple wrapper around
the <TT
CLASS="COMMAND"
>CREATE LANGUAGE</TT
> command. It eases
installation of procedural languages from the shell command line.
</P
><P
> Use <A
HREF="sql-droplanguage.html"
><I
>DROP LANGUAGE</I
></A
>, or better yet the <A
HREF="app-droplang.html"
><SPAN
CLASS="APPLICATION"
>droplang</SPAN
></A
> program, to drop procedural languages.
</P
><P
> The system catalog <CODE
CLASS="CLASSNAME"
>pg_language</CODE
> (see <A
HREF="catalog-pg-language.html"
>Section 44.21</A
>) records information about the
currently installed languages. Also, <TT
CLASS="COMMAND"
>createlang</TT
>
has an option to list the installed languages.
</P
><P
> To create functions in a procedural language, a user must have the
<TT
CLASS="LITERAL"
>USAGE</TT
> privilege for the language. By default,
<TT
CLASS="LITERAL"
>USAGE</TT
> is granted to <TT
CLASS="LITERAL"
>PUBLIC</TT
> (i.e., everyone)
for trusted languages. This can be revoked if desired.
</P
><P
> Procedural languages are local to individual databases.
However, a language can be installed into the <TT
CLASS="LITERAL"
>template1</TT
>
database, which will cause it to be available automatically in
all subsequently-created databases.
</P
><P
> The call handler function and the validator function (if any)
must already exist if the server does not have an entry for the language
in <TT
CLASS="STRUCTNAME"
>pg_pltemplate</TT
>. But when there is an entry,
the functions need not already exist;
they will be automatically defined if not present in the database.
(This might result in <TT
CLASS="COMMAND"
>CREATE LANGUAGE</TT
> failing, if the
shared library that implements the language is not available in
the installation.)
</P
><P
> In <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> versions before 7.3, it was
necessary to declare handler functions as returning the placeholder
type <TT
CLASS="TYPE"
>opaque</TT
>, rather than <TT
CLASS="TYPE"
>language_handler</TT
>.
To support loading
of old dump files, <TT
CLASS="COMMAND"
>CREATE LANGUAGE</TT
> will accept a function
declared as returning <TT
CLASS="TYPE"
>opaque</TT
>, but it will issue a notice and
change the function's declared return type to <TT
CLASS="TYPE"
>language_handler</TT
>.
</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="SQL-CREATELANGUAGE-EXAMPLES"
></A
><H2
>Examples</H2
><P
> The preferred way of creating any of the standard procedural languages
is just:
</P><PRE
CLASS="PROGRAMLISTING"
>CREATE LANGUAGE plpgsql;</PRE
><P>
</P
><P
> For a language not known in the <TT
CLASS="STRUCTNAME"
>pg_pltemplate</TT
> catalog, a
sequence such as this is needed:
</P><PRE
CLASS="PROGRAMLISTING"
>CREATE FUNCTION plsample_call_handler() RETURNS language_handler
AS '$libdir/plsample'
LANGUAGE C;
CREATE LANGUAGE plsample
HANDLER plsample_call_handler;</PRE
><P>
</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="SQL-CREATELANGUAGE-COMPAT"
></A
><H2
>Compatibility</H2
><P
> <TT
CLASS="COMMAND"
>CREATE LANGUAGE</TT
> is a
<SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> extension.
</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN52860"
></A
><H2
>See Also</H2
><A
HREF="sql-alterlanguage.html"
><I
>ALTER LANGUAGE</I
></A
>, <A
HREF="sql-createfunction.html"
><I
>CREATE FUNCTION</I
></A
>, <A
HREF="sql-droplanguage.html"
><I
>DROP LANGUAGE</I
></A
>, <A
HREF="sql-grant.html"
><I
>GRANT</I
></A
>, <A
HREF="sql-revoke.html"
><I
>REVOKE</I
></A
>, <A
HREF="app-createlang.html"
><I
><I
>createlang</I
></I
></A
>, <A
HREF="app-droplang.html"
><I
><I
>droplang</I
></I
></A
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