Before update oracle trigger problem [PL/SQL]

Question

Table:

CREATE TABLE EXAMPLE1 (column1 integer, column2 integer, column3 integer);

Insert:

INSERT INTO EXAMPLE1 VALUES (1,11,111);

Trigger:

create or replace TRIGGER trigger_name
BEFORE UPDATE OF COLUMN1 ON EXAMPLE1
FOR EACH ROW
BEGIN
    RAISE_APPLICATION_ERROR(-20000, 'You can't directly update this column.');
END;

Update:

UPDATE EXAMPLE1 SET COLUMN1 = 2 WHERE COLUMN2 = 11;

So, when I try to update the column1 (column1 = 2) trigger should execute and tell me that I can't directly change that column, but if I execute a query like this:

UPDATE EXAMPLE1 SET column1 = 1, column2 = 22 where column3 = 111;

I mean where I send also column1 = 1 (column1 is equal to 1) so there is no changing of value, it should update the table because I'm changing just column2, column1 stays unchanged equal to 1.

Answer 1

you are still updating the column no matter what the new value is, in your trigger you have to check if the value is changing or not:

CREATE OR REPLACE TRIGGER trigger_name
BEFORE UPDATE OF COLUMN1 ON EXAMPLE1
FOR EACH ROW
BEGIN
    IF DECODE(:new.column1, :old.column1, 1, 0) = 0 THEN
      RAISE_APPLICATION_ERROR(-20000, 'You can''t directly update this column.')
    END IF
END;

Answer 2

Use when clause as follows:

CREATE OR REPLACE TRIGGER trigger_name
BEFORE UPDATE OF COLUMN1 ON EXAMPLE1
FOR EACH ROW
WHEN ( NEW.COLUMN1 <> OLD.COLUMN1 
       OR NOT (NEW.COLUMN1 IS NULL AND OLD.COLUMN1 IS NULL)
      ) 
BEGIN
      RAISE_APPLICATION_ERROR(-20000, 'You can''t directly update this column.');
END;
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