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PostgreSQL – ALTER TRIGGER
  • Last Updated : 28 Aug, 2020

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:

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