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<refentry id="SQL-SET-SESSION-AUTHORIZATION">
 <docinfo>
  <date>2001-04-21</date>
 </docinfo>

 <refmeta>
  <refentrytitle id="sql-set-session-authorization-title">SET SESSION AUTHORIZATION</refentrytitle>
  <refmiscinfo>SQL - Language Statements</refmiscinfo>
 </refmeta>

 <refnamediv>
  <refname>SET SESSION AUTHORIZATION</refname>
  <refpurpose>set the session user identifier and the current user identifier of the current session</refpurpose>
 </refnamediv>

 <refsynopsisdiv>
<synopsis>
SET [ SESSION | LOCAL ] SESSION AUTHORIZATION <replaceable class="PARAMETER">username</replaceable>
SET [ SESSION | LOCAL ] SESSION AUTHORIZATION DEFAULT
RESET SESSION AUTHORIZATION
</synopsis>
 </refsynopsisdiv>

 <refsect1>
  <title>Description</title>

  <para>
   This command sets the session user identifier and the current user
   identifier of the current SQL-session context to be <replaceable
   class="PARAMETER">username</replaceable>.  The user name may be
   written as either an identifier or a string literal.  The session
   user identifier is valid for the duration of a connection; for
   example, it is possible to temporarily become an unprivileged user
   and later switch back to become a superuser.
  </para>

  <para>
   The session user identifier is initially set to be the (possibly
   authenticated) user name provided by the client.  The current user
   identifier is normally equal to the session user identifier, but
   may change temporarily in the context of <quote>setuid</quote>
   functions and similar mechanisms.  The current user identifier is
   relevant for permission checking.
  </para>

  <para>
   The session user identifier may be changed only if the initial session
   user (the <firstterm>authenticated user</firstterm>) had the
   superuser privilege.  Otherwise, the command is accepted only if it
   specifies the authenticated user name.
  </para>

  <para>
   The <option>SESSION</> and <option>LOCAL</> modifiers act the same
   as for the regular <xref linkend="SQL-SET" endterm="SQL-SET-title">
   command.
  </para>

  <para>
   The <literal>DEFAULT</> and <literal>RESET</> forms reset the session
   and current user identifiers to be the originally authenticated user
   name.  These forms are always accepted.
  </para>

 </refsect1>

 <refsect1>
  <title>Examples</title>

<programlisting>
SELECT SESSION_USER, CURRENT_USER;

 session_user | current_user 
--------------+--------------
 peter        | peter

SET SESSION AUTHORIZATION 'paul';

SELECT SESSION_USER, CURRENT_USER;

 session_user | current_user 
--------------+--------------
 paul         | paul
</programlisting>
 </refsect1>

 <refsect1>
  <title>Compatibility</title>

  <simpara>SQL99</simpara>

  <para>
   SQL99 allows some other expressions to appear in place of the
   literal <parameter>username</parameter> which are not important in
   practice.  <application>PostgreSQL</application> allows identifier
   syntax (<literal>"username"</literal>), which SQL does not.  SQL
   does not allow this command during a transaction;
   <application>PostgreSQL</application> does not make
   this restriction because there is no reason to.  The
   privileges necessary to execute this command are left
   implementation-defined by the standard.
  </para>
 </refsect1>
</refentry>

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