Question

I would like to ask a question about triggers. Let’s say that I have a table T and I need a trigger before update. However, I have a problem. I need to check a condition using the other rows of T from the trigger. My question is: Which RDBMS’s support this? Where can I write triggers which perform selection(s) on the same table where the trigger fires. For instance:

CREATE TRIGGER updtrigger BEFORE UPDATE ON Employee
    -> FOR EACH ROW
    -> BEGIN
    -> IF NEW.Salary<=500 THEN
    -> SET NEW.Salary=10000;
    -> ELSEIF NEW.Salary>500 and NEW.Salary < 600 THEN
    -> SET NEW.Salary=15000;
    -> ELSEIF NEW.Salary > (select MAX(Salary) from Employee)
    -> Set NEW.Salary = 601;
    -> END IF;
    -> END
    -> //

Thank you,

Best regards,

Lajos Arpad.

Answer 1

The given trigger will throw an Mutating table exception in Oracle, for example, but there is a solution in Oracle, for instance this trigger is allowed and it works fine:

CREATE or replace TRIGGER updtrigger BEFORE UPDATE ON Employees
     FOR EACH ROW
DECLARE
 pragma autonomous_transaction;
 n number;
     BEGIN
     select MAX(Salary) into n from Employees;
     IF :NEW.Salary<=500 THEN
          DBMS_OUTPUT.PUT_LINE('kisebb mint 500');
          :NEW.salary:=n;
    end if;
commit;
     END;