CREATE TRIGGER - Creates a new trigger
SYNOPSIS
CREATE TRIGGER name { BEFORE | AFTER } { event [OR ...] }
ON table FOR EACH { ROW | STATEMENT }
EXECUTE PROCEDURE func ( arguments )
INPUTS
name The name of an existing trigger.
table The name of a table.
event One of INSERT, DELETE or UPDATE.
func A user-supplied function.
OUTPUTS
CREATE This message is returned if the trigger is success
fully created.
DESCRIPTION
CREATE TRIGGER will enter a new trigger into the current
data base. The trigger will be associated with the rela
tion table and will execute the specified function func.
The trigger can be specified to fire either before BEFORE
the operation is attempted on a tuple (before constraints
are checked and the INSERT, UPDATE or DELETE is attempted)
or AFTER the operation has been attempted (e.g., after
constraints are checked and the INSERT, UPDATE or DELETE
has completed). If the trigger fires before the event, the
trigger may skip the operation for the current tuple, or
change the tuple being inserted (for INSERT and UPDATE
operations only). If the trigger fires after the event,
all changes, including the last insertion, update, or
deletion, are "visible" to the trigger.
Refer to the chapters on SPI and Triggers in the Post
greSQL Programmer's Guide for more information.
NOTES
CREATE TRIGGER is a Postgres language extension.
Only the relation owner may create a trigger on this rela
tion.
As of the current release (v7.0), STATEMENT triggers are
not implemented.
triggers.
USAGE
Check if the specified distributor code exists in the dis
tributors table before appending or updating a row in the
table films:
CREATE TRIGGER if_dist_exists
BEFORE INSERT OR UPDATE ON films FOR EACH ROW
EXECUTE PROCEDURE check_primary_key ('did', 'distributors', 'did');
Before cancelling a distributor or updating its code,
remove every reference to the table films:
CREATE TRIGGER if_film_exists
BEFORE DELETE OR UPDATE ON distributors FOR EACH ROW
EXECUTE PROCEDURE check_foreign_key (1, 'CASCADE', 'did', 'films', 'did');
COMPATIBILITY
SQL92
There is no CREATE TRIGGER in SQL92.
The second example above may also be done by using a FOR
EIGN KEY constraint as in:
CREATE TABLE distributors (
did DECIMAL(3),
name VARCHAR(40),
CONSTRAINT if_film_exists
FOREIGN KEY(did) REFERENCES films
ON UPDATE CASCADE ON DELETE CASCADE
);
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