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LISTEN()			 SQL Commands			      LISTEN()

       LISTEN - listen for a notification

       LISTEN name

       LISTEN  registers the current session as a listener on the notification
       condition name.	If the current session is already registered as a lis-
       tener 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 programming 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
       interfaces 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.

       name   Name of a notify condition (any identifier).

       Configure and execute a listen/notify sequence from psql:

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

       There is no LISTEN statement in the SQL standard.

       NOTIFY [notify(7)], UNLISTEN [unlisten(l)]

SQL - Language Statements	  2010-12-14			      LISTEN()