PostgreSQL DROP TRIGGER

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.

Second, use 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., schema_name.table_name.

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 RESTRICT.

Note that in SQL standard, trigger names are not local to tables so the statement is simply:

DROP TRIGGER trigger_name;

PostgreSQL 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 username_check trigger:

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.

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