LISTEN(7)                                                 SQL Commands                                                 LISTEN(7)



NAME
       LISTEN - listen for a notification


SYNOPSIS
       LISTEN name


DESCRIPTION
       LISTEN registers the current session as a listener on the notification condition name.  If the current session is already
       registered as a listener for this notification condition, nothing is done.

       Whenever the command NOTIFY name is invoked, either by this session or another one connected to the  same  database,  all
       the  sessions currently listening on that notification condition are notified, and each will in turn notify its connected
       client application. See the discussion of NOTIFY for more information.

       A session can be unregistered for a given notify condition with the UNLISTEN command. A  session's  listen  registrations
       are automatically cleared when the session ends.

       The  method  a client application must use to detect notification events depends on which PostgreSQL application program-
       ming interface it uses. With the libpq library, the application issues LISTEN as an ordinary SQL command, and  then  must
       periodically  call  the  function PQnotifies to find out whether any notification events have been received. Other inter-
       faces such as libpgtcl provide higher-level methods for handling notify events; indeed,  with  libpgtcl  the  application
       programmer  should  not even issue LISTEN or UNLISTEN directly. See the documentation for the interface you are using for
       more details.

       NOTIFY [notify(7)] contains a more extensive discussion of the use of LISTEN and NOTIFY.

PARAMETERS
       name   Name of a notify condition (any identifier).

EXAMPLES
       Configure and execute a listen/notify sequence from psql:

       LISTEN virtual;
       NOTIFY virtual;
       Asynchronous notification "virtual" received from server process with PID 8448.


COMPATIBILITY
       There is no LISTEN statement in the SQL standard.

SEE ALSO
       NOTIFY [notify(7)], UNLISTEN [unlisten(7)]



SQL - Language Statements                                  2011-09-22                                                  LISTEN(7)