1LISTEN()                         SQL Commands                         LISTEN()
2
3
4

NAME

6       LISTEN - listen for a notification
7
8

SYNOPSIS

10       LISTEN name
11
12

DESCRIPTION

14       LISTEN  registers the current session as a listener on the notification
15       condition name.  If the current session is already registered as a lis‐
16       tener for this notification condition, nothing is done.
17
18       Whenever  the command NOTIFY name is invoked, either by this session or
19       another one connected to the same database, all the sessions  currently
20       listening on that notification condition are notified, and each will in
21       turn notify its connected client application.  See  the  discussion  of
22       NOTIFY for more information.
23
24       A  session  can  be  unregistered for a given notify condition with the
25       UNLISTEN command. A session's listen  registrations  are  automatically
26       cleared when the session ends.
27
28       The  method a client application must use to detect notification events
29       depends on which PostgreSQL application programming interface it  uses.
30       With  the  libpq  library, the application issues LISTEN as an ordinary
31       SQL command, and then must periodically call the function PQnotifies to
32       find  out  whether  any  notification  events have been received. Other
33       interfaces such as libpgtcl provide higher-level methods  for  handling
34       notify  events; indeed, with libpgtcl the application programmer should
35       not even issue LISTEN or UNLISTEN directly. See the  documentation  for
36       the interface you are using for more details.
37
38       NOTIFY  [notify(7)]  contains a more extensive discussion of the use of
39       LISTEN and NOTIFY.
40

PARAMETERS

42       name   Name of a notify condition (any identifier).
43

EXAMPLES

45       Configure and execute a listen/notify sequence from psql:
46
47       LISTEN virtual;
48       NOTIFY virtual;
49       Asynchronous notification "virtual" received from server process with PID 8448.
50
51

COMPATIBILITY

53       There is no LISTEN statement in the SQL standard.
54

SEE ALSO

56       NOTIFY [notify(7)], UNLISTEN [unlisten(l)]
57
58
59
60SQL - Language Statements         2008-06-08                          LISTEN()
Impressum