CREATE TRIGGER() SQL Commands CREATE TRIGGER()NAME
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 successfully created.
DESCRIPTION
CREATE TRIGGER will enter a new trigger into the current data base. The
trigger will be associated with the relation 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 inser‐
tion, update, or deletion, are "visible" to the trigger.
Refer to the chapters on SPI and Triggers in the PostgreSQL Program‐
mer's Guide for more information.
NOTES
CREATE TRIGGER is a Postgres language extension.
Only the relation owner may create a trigger on this relation.
As of the current release (v7.0), STATEMENT triggers are not imple‐
mented.
Refer to DROP TRIGGER for information on how to remove triggers.
USAGE
Check if the specified distributor code exists in the distributors ta‐
ble 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 ref‐
erence 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 FOREIGN KEY con‐
straint 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
);
SQL - Language Statements 29 March 2001 CREATE TRIGGER()
