Summary: in this tutorial, you will learn how to use the PostgreSQL
DROP TRIGGER to drop a trigger from a table.
Introduction to PostgreSQL
DROP TRIGGER statement
To delete a trigger from a table, you use the
DROP TRIGGER statement with the following syntax:
DROP TRIGGER [IF EXISTS] trigger_name ON table_name [ CASCADE | RESTRICT ];
In this syntax:
First, specify the name of the trigger which you want to delete after the
DROP TRIGGER keywords.
IF EXISTS to conditionally delete the trigger only if it exists. Attempt to delete a non-existing trigger without specifying the
IF EXISTS statement results in an error. If you use
IF EXISTS to delete a non-existing trigger, PostgreSQL issues a notice instead.
Third, specify the name of the table to which the trigger belongs. If the table belongs to a specific schema, you can use the schema-qualified name of the table e.g.,
Fourth, use the
CASCADE option if you want to drop objects that depend on the trigger automatically. Note that
CASCADE option will also delete objects that depend on objects that depend on the trigger.
Fifth, use the
RESTRICT option to refuse to drop the trigger if any objects depend on it. By default, the
DROP TRIGGER statement uses
Note that in SQL standard, trigger names are not local to tables so the statement is simply:
DROP TRIGGER trigger_name;
DROP TRIGGER example
First, create a function that validates the username of a staff. The username of staff must not be null and its length must be at least 8.
CREATE FUNCTION check_staff_user() RETURNS TRIGGER AS $$ BEGIN IF length(NEW.username) < 8 OR NEW.username IS NULL THEN RAISE EXCEPTION 'The username cannot be less than 8 characters'; END IF; IF NEW.NAME IS NULL THEN RAISE EXCEPTION 'Username cannot be NULL'; END IF; RETURN NEW; END; $$ LANGUAGE plpgsql;
Second, create a new trigger on the staff table to check the username of a staff. This trigger will fire whenever you insert or update a row in the staff table (from the sample database) :
CREATE TRIGGER username_check BEFORE INSERT OR UPDATE ON staff FOR EACH ROW EXECUTE PROCEDURE check_staff_user();
Third, use the
DROP TRIGGER statement to delete the
DROP TRIGGER username_check ON staff;
In this tutorial, you have learned how to use the PostgreSQL
DROP TRIGGER statement to delete a trigger from a table.