PostgreSQL – ALTER TRIGGER
In PostgreSQL, to modify the trigger, you use ALTER TRIGGER statement. This statement is a PostgreSQL extension of the SQL standard. The syntax of the ALTER TRIGGER statement is as follows:
Syntax:
ALTER TRIGGER trigger_name ON table_name
RENAME TO new_name;
Let’s analyze the above syntax:
- First, specify the name of a trigger associated with a particular table that you want to change.
- Second, put the new trigger name in the RENAME TO clause.
Example:
First, we create a staff table for demonstration with the below statement:
CREATE TABLE staff( user_id serial PRIMARY KEY, username VARCHAR (50) UNIQUE NOT NULL, password VARCHAR (50) NOT NULL, email VARCHAR (355) UNIQUE NOT NULL, created_on TIMESTAMP NOT NULL, last_login TIMESTAMP );
Second, 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;
Third, 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.
CREATE TRIGGER username_check BEFORE INSERT OR UPDATE ON staff FOR EACH ROW EXECUTE PROCEDURE check_staff_user();
Now to modify the above-created trigger use the below statement:
ALTER TRIGGER username_check ON staff RENAME TO check_username;
Output: