listen(7) - phpMan

LISTEN()                                   SQL Commands                                  LISTEN()



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 con-
       nected 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 applica-
       tion  issues  LISTEN as an ordinary SQL command, and then must periodically call the func-
       tion 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(l)]



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

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