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>Chapter 37. Procedural Languages</TD
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CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="XPLANG-INSTALL"
>37.1. 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, it is
    only necessary to execute <TT
CLASS="COMMAND"
>CREATE LANGUAGE</TT
>
    <TT
CLASS="REPLACEABLE"
><I
>language_name</I
></TT
> to install the language into the
    current database.  Alternatively, the program <A
HREF="app-createlang.html"
><SPAN
CLASS="APPLICATION"
>createlang</SPAN
></A
> can be used to do this from the shell
    command line.  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"
>CREATE LANGUAGE</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.  (For languages
     known to <TT
CLASS="COMMAND"
>CREATE LANGUAGE</TT
>, the second and third steps
     can be omitted, because they will be carried out automatically
     if needed.)
    </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 34.9.6</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 can 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-install.html#XPLANG-INSTALL-EXAMPLE"
>Example 37-1</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 37-1. 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 the <SPAN
CLASS="APPLICATION"
>PL/PythonU</SPAN
> handler is
    installed if Python support is configured.
   </P
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