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<!-- $Header: /cvsroot/pgsql/doc/src/sgml/ref/set_session_auth.sgml,v 1.7 2002/09/21 18:32:54 petere Exp $ -->
<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 <parameter>username</parameter>
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
<parameter>username</parameter>. 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>
<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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