unlisten.sgml

PostgreSQL 8.1.4的源码 适用于Linux下的开源数据库系统

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$PostgreSQL: pgsql/doc/src/sgml/ref/unlisten.sgml,v 1.27 2003/11/29 19:51:39 pgsql Exp $
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<refentry id="SQL-UNLISTEN">
 <refmeta>
  <refentrytitle id="SQL-UNLISTEN-TITLE">UNLISTEN</refentrytitle>
  <refmiscinfo>SQL - Language Statements</refmiscinfo>
 </refmeta>

 <refnamediv>
  <refname>UNLISTEN</refname>
  <refpurpose>stop listening for a notification</refpurpose>
 </refnamediv>

 <indexterm zone="sql-unlisten">
  <primary>UNLISTEN</primary>
 </indexterm>

 <refsynopsisdiv>
<synopsis>
UNLISTEN { <replaceable class="PARAMETER">name</replaceable> | * }
</synopsis>
 </refsynopsisdiv>

 <refsect1>
  <title>Description</title>

  <para>
   <command>UNLISTEN</command> is used to remove an existing
   registration for <command>NOTIFY</command> events.
   <command>UNLISTEN</command> cancels any existing registration of
   the current <productname>PostgreSQL</productname> session as a
   listener on the notification <replaceable
   class="PARAMETER">name</replaceable>.  The special wildcard
   <literal>*</literal> cancels all listener registrations for the
   current session.
  </para>

  <para>
   <xref endterm="sql-notify-title" linkend="sql-notify">
   contains a more extensive
   discussion of the use of <command>LISTEN</command> and
   <command>NOTIFY</command>.
  </para>
 </refsect1>

 <refsect1>
  <title>Parameters</title>

  <variablelist>
   <varlistentry>
    <term><replaceable class="PARAMETER">name</replaceable></term>
    <listitem>
     <para>
      Name of a notification (any identifier).
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>*</literal></term>
    <listitem>
     <para>
      All current listen registrations for this session are cleared.
     </para>
    </listitem>
   </varlistentry>
  </variablelist>
 </refsect1>

 <refsect1>
  <title>Notes</title>

  <para>
   You may unlisten something you were not listening for; no warning or error
   will appear.
  </para>

  <para>
   At the end of each session, <command>UNLISTEN *</command> is
   automatically executed.
  </para>
 </refsect1>

 <refsect1>
  <title>Examples</title>

  <para>
   To make a registration:

<programlisting>
LISTEN virtual;
NOTIFY virtual;
Asynchronous notification "virtual" received from server process with PID 8448.
</programlisting>
  </para>

  <para>
   Once <command>UNLISTEN</> has been executed, further <command>NOTIFY</>
   commands will be ignored:

<programlisting>
UNLISTEN virtual;
NOTIFY virtual;
-- no NOTIFY event is received
</programlisting>
  </para>
 </refsect1>

 <refsect1>
  <title>Compatibility</title>

  <para>
   There is no <command>UNLISTEN</command> command in the SQL standard.
  </para>
 </refsect1>

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

  <simplelist type="inline">
   <member><xref linkend="sql-listen" endterm="sql-listen-title"></member>
   <member><xref linkend="sql-notify" endterm="sql-notify-title"></member>
  </simplelist>
 </refsect1>
</refentry>

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