Field != then Insert Into Other Table

Question

Hi,
I cannot figure out how to create a trigger that will insert data based on if a old.field != new.field. If the field was changed in
one table tbl_test then insert that record into the other table tbl_test_history. This is a little different since I want to insert a record if a update
took place. The update will still take place in tbl_test but I want a insert to take place in tbl_test_history.
CREATE OR REPLACE TRIGGER AU_INSERT_TEST_HISTORY
  AFTER UPDATE
  ON TBL_TEST   FOR EACH ROW
WHEN (
    OLD.Orange != NEW.Orange
OR OLD.Apple != NEW.Apple
BEGIN
INSERT INTO TBL_TEST_HISTORY
(ORANGE,
  APPLE
  BANANA,
  GRAPE
  select ORANGE,
         APPLE
         BANANA,
         GRAPE
FROM TBL_TEST, TBL_TEST_HISTORY
  WHERE  TBL_TEST.PK_TEST_ID = TBL_TEST_HISTORY.PK_TEST_ID;
END AU_INSERT_TEST_HISTORY;
/I will have a separate trigger that will insert records from tbl_test to tbl_test_history. This trigger compiles with no errors but when I
create a record in tbl_test I receive an error. I am not sure if the syntax is correct, can anyone help me with this?

Answer 1

My bad. I put the colon : into the when clause. They weren't there in your code. Usually I use an if condition, which is a little different.
I added some NVL logic to to consider comparison of NULL values too.
CREATE OR REPLACE TRIGGER AU_INSERT_TEST_HISTORY
  AFTER UPDATE  ON TBL_TEST  
  FOR EACH ROW
BEGIN
  if nvl(:old.ORANGE,'xxx') != nvl(:new.ORANGE,'yyy')
     OR nvl(:old.APPLE,'xxx') != nvl(:new.APPLE,'yyy')
  then
    INSERT INTO TBL_TEST_HISTORY
     (ORANGE, APPLE, BANANA, GRAPE)
    values (:new.ORANGE,
             :new.APPLE,
             :new.BANANA,
             :new.GRAPE);
  end if;
END AU_INSERT_TEST_HISTORY;
/ You can additionally consider to make this trigger an AFTER INSERT OR UPDATE trigger.
Then you would also put the inserted values from the start into your history table.
Edited by: Sven W. on Aug 9, 2012 4:14 PM