Question

I am trying to use a trigger to avoid a deletion of a row in table Products under some circumstances. The code is the following

CREATE TRIGGER trgPreventProductRemoval
    BEFORE DELETE ON Products
    FOR EACH ROW

    BEGIN
        DECLARE
            l_custid INTEGER;
        BEGIN
            SELECT count(*) INTO l_custid FROM Orders WHERE product = :old.prodDescription ;

            IF l_custid > 0 THEN
                raise_application_error (-20100, 'You can not delete a product that has active orders!');
            END IF;
        END;
    END;

However I get the error: table ORDERS is mutating, trigger/function may not see it.

How can I fix it?

EDIT-SOLUTION: I have accepted the solution below because it is the “politically correct”. Due to some “restrictions” I was unable to use it and finally found a different workaround. See the solution that I have posted seperately.

Answer 1

Use a foreign key between Orders and Product table instead of a trigger.