在触发器SQL中更新名称（与以前不同）

Question

I'm writing a trigger for a company database, and this trigger is intended to update a name of an employee (in the rare case of changing name for example) that should be different from a previous one, or NOT NULL.

This is the code I wrote. It compiles but it gives me error on the update (ORA-04091: table COMPANY.EMPLOYEE is mutating, trigger/function may not see it). I've noticed that is caused by FOR EACH ROW , but I cannot remove that because otherwise the :new and :old references will not work.

CREATE OR REPLACE TRIGGER NO_INVALID_NAME
AFTER UPDATE OF EMPLOYEE_NAME ON EMPLYEE 
FOR EACH ROW
DECLARE
  INVALID_NAME EXCEPTION;
  CORRECT_NAME EXCEPTION;

BEGIN
  UPDATE EMPLOYEE 
  SET EMPLOYEE_NAME =:NEW.EMPLOYEE_NAME
  WHERE EMPLOYEE_NAME =:OLD.EMPLOYEE_NAME;

  IF :NEW.EMPLOYEE_NAME <> :OLD.EMPLOYEE_NAME AND IS NOT NULL THEN
    RAISE INVALID_NAME;
  ELSE
    RAISE CORRECT_NAME;
  END IF;

EXCEPTION
  WHEN NOME_NON_CORRETTO
    THEN RAISE_APPLICATION_ERROR(-20009,'Name cannot be updated.');
  WHEN CORRECT_NAME 
    THEN DBMS_OUTPUT.PUT_LINE('Updated.');
END;

i guess i'm messing up something with the :NEW and :OLD statement, but i can't see where.

Answer 1

There is a typo in the table name in the 2nd line, so let's change it to EMPLOYEE.

AFTER UPDATE OF EMPLOYEE_NAME ON EMPLOYEE

I would try to add :NEW.EMPLOYEE_NAME before IS NOT NULL clause, but I am sure if it fixes all the problems.

IF(:NEW.EMPLOYEE_NAME <> :OLD.EMPLOYEE_NAME AND :NEW.EMPLOYEE_NAME IS NOT NULL)

Answer 2

In the trigger you do the same operation like in the update. So - the "application" makes an update (without commit) then the trigger makes the same update and then it verifies the :new.name and the old.name .

Try this:

CREATE OR REPLACE TRIGGER NO_INVALID_NAME
BEFORE UPDATE ON EMPLOYEE 
FOR EACH ROW
DECLARE
    INVALID_NAME EXCEPTION;
    CORRECT_NAME EXCEPTION;
BEGIN
    IF :NEW.EMPLOYEE_NAME <> :OLD.EMPLOYEE_NAME AND :NEW.EMPLOYEE_NAME IS NOT NULL THEN
        RAISE INVALID_NAME;
    ELSE
        RAISE CORRECT_NAME;
    END IF;
EXCEPTION
    WHEN NOME_NON_CORRETTO
        THEN RAISE_APPLICATION_ERROR(-20009,'Name cannot be updated.');
    WHEN CORRECT_NAME 
        THEN DBMS_OUTPUT.PUT_LINE('Updated.');
END;