listen

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 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.

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)