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>PostgreSQL 8.0.11 Documentation</TH
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><DIV
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><H1
><A
NAME="XPLANG"
></A
>Chapter 34. Procedural Languages</H1
><A
NAME="AEN32246"
></A
><P
> <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> allows user-defined functions
to be written in other languages besides SQL and C. These other
languages are generically called <I
CLASS="FIRSTTERM"
>procedural
languages</I
> (<ACRONYM
CLASS="ACRONYM"
>PL</ACRONYM
>s). For a function
written in a procedural language, the database server has
no built-in knowledge about how to interpret the function's source
text. Instead, the task is passed to a special handler that knows
the details of the language. The handler could either do all the
work of parsing, syntax analysis, execution, etc. itself, or it
could serve as <SPAN
CLASS="QUOTE"
>"glue"</SPAN
> between
<SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> and an existing implementation
of a programming language. The handler itself is a
C language function compiled into a shared object and
loaded on demand, just like any other C function.
</P
><P
> There are currently four procedural languages available in the
standard <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> distribution:
<SPAN
CLASS="APPLICATION"
>PL/pgSQL</SPAN
> (<A
HREF="plpgsql.html"
>Chapter 35</A
>),
<SPAN
CLASS="APPLICATION"
>PL/Tcl</SPAN
> (<A
HREF="pltcl.html"
>Chapter 36</A
>),
<SPAN
CLASS="APPLICATION"
>PL/Perl</SPAN
> (<A
HREF="plperl.html"
>Chapter 37</A
>), and
<SPAN
CLASS="APPLICATION"
>PL/Python</SPAN
> (<A
HREF="plpython.html"
>Chapter 38</A
>).
Other languages can be defined by users.
The basics of developing a new procedural language are covered in <A
HREF="plhandler.html"
>Chapter 45</A
>.
</P
><P
> There are additional procedural languages available that are not
included in the core distribution. <A
HREF="external-projects.html"
>Appendix H</A
>
has information about finding them.
</P
><DIV
CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="XPLANG-INSTALL"
>34.1. Installing Procedural Languages</A
></H1
><P
> A procedural language must be <SPAN
CLASS="QUOTE"
>"installed"</SPAN
> into each
database where it is to be used. But procedural languages installed in
the database <TT
CLASS="LITERAL"
>template1</TT
> are automatically available in all
subsequently created databases, since their entries in
<TT
CLASS="LITERAL"
>template1</TT
> will be copied by <TT
CLASS="COMMAND"
>CREATE DATABASE</TT
>.
So the database administrator can
decide which languages are available in which databases and can make
some languages available by default if he chooses.
</P
><P
> For the languages supplied with the standard distribution, the
program <A
HREF="app-createlang.html"
><SPAN
CLASS="APPLICATION"
>createlang</SPAN
></A
> may be used to install the
language instead of carrying out the details by hand. For
example, to install the language
<SPAN
CLASS="APPLICATION"
>PL/pgSQL</SPAN
> into the database
<TT
CLASS="LITERAL"
>template1</TT
>, use
</P><PRE
CLASS="PROGRAMLISTING"
>createlang plpgsql template1</PRE
><P>
The manual procedure described below is only recommended for
installing custom languages that <TT
CLASS="COMMAND"
>createlang</TT
>
does not know about.
</P
><DIV
CLASS="PROCEDURE"
><P
><B
> Manual Procedural Language Installation
</B
></P
><P
> A procedural language is installed in a database in four steps,
which must be carried out by a database superuser. The
<TT
CLASS="COMMAND"
>createlang</TT
> program automates all but <A
HREF="xplang.html#XPLANG-INSTALL-CR1"
>step 1</A
>.
</P
><OL
TYPE="1"
><LI
CLASS="STEP"
><A
NAME="XPLANG-INSTALL-CR1"
></A
><P
> The shared object for the language handler must be compiled and
installed into an appropriate library directory. This works in the same
way as building and installing modules with regular user-defined C
functions does; see <A
HREF="xfunc-c.html#DFUNC"
>Section 31.9.6</A
>. Often, the language
handler will depend on an external library that provides the actual
programming language engine; if so, that must be installed as well.
</P
></LI
><LI
CLASS="STEP"
><A
NAME="XPLANG-INSTALL-CR2"
></A
><P
> The handler must be declared with the command
</P><PRE
CLASS="SYNOPSIS"
>CREATE FUNCTION <TT
CLASS="REPLACEABLE"
><I
>handler_function_name</I
></TT
>()
RETURNS language_handler
AS '<TT
CLASS="REPLACEABLE"
><I
>path-to-shared-object</I
></TT
>'
LANGUAGE C;</PRE
><P>
The special return type of <TT
CLASS="TYPE"
>language_handler</TT
> tells
the database system that this function does not return one of
the defined <ACRONYM
CLASS="ACRONYM"
>SQL</ACRONYM
> data types and is not directly usable
in <ACRONYM
CLASS="ACRONYM"
>SQL</ACRONYM
> statements.
</P
></LI
><LI
CLASS="STEP"
><A
NAME="XPLANG-INSTALL-CR3"
></A
><P
> Optionally, the language handler may provide a <SPAN
CLASS="QUOTE"
>"validator"</SPAN
>
function that checks a function definition for correctness without
actually executing it. The validator function is called by
<TT
CLASS="COMMAND"
>CREATE FUNCTION</TT
> if it exists. If a validator function
is provided by the handler, declare it with a command like
</P><PRE
CLASS="SYNOPSIS"
>CREATE FUNCTION <TT
CLASS="REPLACEABLE"
><I
>validator_function_name</I
></TT
>(oid)
RETURNS void
AS '<TT
CLASS="REPLACEABLE"
><I
>path-to-shared-object</I
></TT
>'
LANGUAGE C;</PRE
><P>
</P
></LI
><LI
CLASS="STEP"
><A
NAME="XPLANG-INSTALL-CR4"
></A
><P
> The PL must be declared with the command
</P><PRE
CLASS="SYNOPSIS"
>CREATE [<SPAN
CLASS="OPTIONAL"
>TRUSTED</SPAN
>] [<SPAN
CLASS="OPTIONAL"
>PROCEDURAL</SPAN
>] LANGUAGE <TT
CLASS="REPLACEABLE"
><I
>language-name</I
></TT
>
HANDLER <TT
CLASS="REPLACEABLE"
><I
>handler_function_name</I
></TT
>
[<SPAN
CLASS="OPTIONAL"
>VALIDATOR <TT
CLASS="REPLACEABLE"
><I
>validator_function_name</I
></TT
></SPAN
>] ;</PRE
><P>
The optional key word <TT
CLASS="LITERAL"
>TRUSTED</TT
> specifies that
ordinary database users that have no superuser privileges should
be allowed to use this language to create functions and trigger
procedures. Since PL functions are executed inside the database
server, the <TT
CLASS="LITERAL"
>TRUSTED</TT
> flag should only be given
for languages that do not allow access to database server
internals or the file system. The languages
<SPAN
CLASS="APPLICATION"
>PL/pgSQL</SPAN
>,
<SPAN
CLASS="APPLICATION"
>PL/Tcl</SPAN
>, and
<SPAN
CLASS="APPLICATION"
>PL/Perl</SPAN
>
are considered trusted; the languages
<SPAN
CLASS="APPLICATION"
>PL/TclU</SPAN
>,
<SPAN
CLASS="APPLICATION"
>PL/PerlU</SPAN
>, and
<SPAN
CLASS="APPLICATION"
>PL/PythonU</SPAN
>
are designed to provide unlimited functionality and should
<SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>not</I
></SPAN
> be marked trusted.
</P
></LI
></OL
></DIV
><P
> <A
HREF="xplang.html#XPLANG-INSTALL-EXAMPLE"
>Example 34-1</A
> shows how the manual
installation procedure would work with the language
<SPAN
CLASS="APPLICATION"
>PL/pgSQL</SPAN
>.
</P
><DIV
CLASS="EXAMPLE"
><A
NAME="XPLANG-INSTALL-EXAMPLE"
></A
><P
><B
>Example 34-1. Manual Installation of <SPAN
CLASS="APPLICATION"
>PL/pgSQL</SPAN
></B
></P
><P
> The following command tells the database server where to find the
shared object for the <SPAN
CLASS="APPLICATION"
>PL/pgSQL</SPAN
> language's call handler function.
</P><PRE
CLASS="PROGRAMLISTING"
>CREATE FUNCTION plpgsql_call_handler() RETURNS language_handler AS
'$libdir/plpgsql' LANGUAGE C;</PRE
><P>
</P
><P
> <SPAN
CLASS="APPLICATION"
>PL/pgSQL</SPAN
> has a validator function,
so we declare that too:
</P><PRE
CLASS="PROGRAMLISTING"
>CREATE FUNCTION plpgsql_validator(oid) RETURNS void AS
'$libdir/plpgsql' LANGUAGE C;</PRE
><P>
</P
><P
> The command
</P><PRE
CLASS="PROGRAMLISTING"
>CREATE TRUSTED PROCEDURAL LANGUAGE plpgsql
HANDLER plpgsql_call_handler
VALIDATOR plpgsql_validator;</PRE
><P>
then defines that the previously declared functions
should be invoked for functions and trigger procedures where the
language attribute is <TT
CLASS="LITERAL"
>plpgsql</TT
>.
</P
></DIV
><P
> In a default <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> installation,
the handler for the <SPAN
CLASS="APPLICATION"
>PL/pgSQL</SPAN
> language
is built and installed into the <SPAN
CLASS="QUOTE"
>"library"</SPAN
>
directory. If <SPAN
CLASS="APPLICATION"
>Tcl</SPAN
> support is configured in, the handlers for
<SPAN
CLASS="APPLICATION"
>PL/Tcl</SPAN
> and <SPAN
CLASS="APPLICATION"
>PL/TclU</SPAN
> are also built and installed in the same
location. Likewise, the <SPAN
CLASS="APPLICATION"
>PL/Perl</SPAN
> and <SPAN
CLASS="APPLICATION"
>PL/PerlU</SPAN
> handlers are built
and installed if Perl support is configured, and <SPAN
CLASS="APPLICATION"
>PL/PythonU</SPAN
> is
installed if Python support is configured.
</P
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