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

 <refmeta>
  <refentrytitle>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 SQL-session context</refpurpose>
 </refnamediv>

 <refsynopsisdiv>
<synopsis>
SET SESSION AUTHORIZATION '<parameter>username</parameter>'
</synopsis>
 </refsynopsisdiv>

 <refsect1>
  <title>Description</title>

  <para>
   This command sets the session user identifier and the current user
   identifer of the current SQL-session context to be
   <parameter>username</parameter>.
  </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 identifer is
   relevant for permission checking.
  </para>

  <para>
   Execution of this command is only permitted if the initial session
   user (the <firstterm>authenticated user</firstterm>) had the
   superuser privilege.  This permission is kept 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>
 </refsect1>

 <refsect1>
  <title>Examples</title>

<screen>
<userinput>SELECT SESSION_USER, CURRENT_USER;</userinput>
 current_user | session_user
--------------+--------------
 peter        | peter

<userinput>SET SESSION AUTHORIZATION 'paul';</userinput>

<userinput>SELECT SESSION_USER, CURRENT_USER;</userinput>
 current_user | session_user
--------------+--------------
 paul         | paul
</screen>
 </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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