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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 regis-
       trations 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  com-
       mand,  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.

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         2014-02-17                         LISTEN(7)