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  cur-
       rently  listening  on that notification condition are notified, and each will in turn notify its connected client application. See the dis-
       cussion 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  PQno-
       tifies  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  docu-
       mentation 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					    2010-05-14								 LISTEN(7)