<literal>PUBLIC</literal> for newly created functions
    (see <xref linkend="ddl-priv"/> for more
    information).  Frequently you will wish to restrict use of a security
    definer function to only some users.  To do that, you must revoke
    the default <literal>PUBLIC</literal> privileges and then grant execute
    privilege selectively.  To avoid having a window where the new function
    is accessible to all, create it and set the privileges within a single
    transaction.  For example:
   </para>

<programlisting>
BEGIN;
CREATE FUNCTION check_password(uname TEXT, pass TEXT) ... SECURITY DEFINER;
REVOKE ALL ON FUNCTION check_password(uname TEXT, pass TEXT) FROM PUBLIC;
GRANT EXECUTE ON FUNCTION check_password(uname TEXT, pass TEXT) TO admins;
COMMIT;
</programlisting>

 </refsect1>

 <refsect1 id="sql-createfunction-compat">
  <title>Compatibility</title>

  <para>
   A <command>CREATE FUNCTION</command> command is defined in the SQL
   standard.  The <productname>PostgreSQL</productname> implementation can be
   used in a compatible way but has many extensions.  Conversely, the SQL
   standard specifies a number of optional features that are not implemented
   in <productname>PostgreSQL</productname>.
  </para>

  <para>
   The following are important compatibility issues:

   <itemizedlist>
    <listitem>
     <para>
      <literal>OR REPLACE</literal> is a PostgreSQL extension.
     </para>
    </listitem>

    <listitem>
     <para>
      For compatibility with some other database systems, <replaceable
      class="parameter">argmode</replaceable> can be written either before or
      after <replaceable class="parameter">argname</replaceable>.  But only
      the first way is standard-compliant.
     </para>
    </listitem>

    <listitem>
     <para>
      For parameter defaults, the SQL standard specifies only the syntax with
      the <literal>DEFAULT</literal> key word.  The syntax with
      <literal>=</literal> is used in T-SQL and Firebird.
     </para>
    </listitem>

    <listitem>
     <para>
      The <literal>SETOF</literal> modifier is a PostgreSQL extension.
     </para>
    </listitem>

    <listitem>
     <para>
      Only <literal>SQL</literal> is standardized as a language.
     </para>
    </listitem>

    <listitem>
     <para>
      All other attributes except <literal>CALLED ON NULL INPUT</literal> and
      <literal>RETURNS NULL ON NULL INPUT</literal> are not standardized.
     </para>
    </listitem>

    <listitem>
     <para>
      For the body of <literal>LANGUAGE SQL</literal> functions, the SQL
      standard only specifies the <replaceable>sql_body</replaceable> form.
     </para>
    </listitem>
   </itemizedlist>
  </para>

  <para>
   Simple <literal>LANGUAGE SQL</literal> functions can be written in a way
   that is both standard-conforming and portable to other implementations.
   More complex functions using advanced features, optimization attributes, or
   other languages will necessarily be specific to PostgreSQL in a significant
   way.
  </para>
 </refsect1>


 <refsect1>
  <title>See Also</title>

  <simplelist type="inline">
   <member><xref linkend="sql-alterfunction"/></member>
   <member><xref linkend="sql-dropfunction"/></member>
   <member><xref linkend="sql-grant"/></member>
   <member><xref linkend="sql-load"/></member>
   <member><xref linkend="sql-revoke"/></member>
  </simplelist>
 </refsect1>

</refentry>