DB Trigger error - Updating same table in the trigger script

Question

Hi All,
I have a table tab1, when ever any update is done on this table on column col1 then col2 also need to get update.(These are linked to forms so user can update only col1 from form frontend)
so I created a trigger as follows.
CREATE OR REPLACE TRIGGER tri1
AFTER UPDATE
ON tab1
FOR EACH ROW
WHEN (NEW.col1 = 'YES')
DECLARE
PRAGMA AUTONOMOUS_TRANSACTION;
BEGIN
UPDATE tab1 SET col2= 1
WHERE transaction_id = :OLD.transaction_id;
COMMIT;
END;
When there is any update on this table I get following error. Please let me know if I miss any thing.
ORA-00060: deadlock detected while waiting for resource
ORA-06512: at "user1.tab1", line 5
ORA-04088: error during execution of trigger 'user1.tab1'
Please let me know if I am not clear. Thanks
Edited by: DharV on Aug 23, 2011 5:17 AM

Answer 1

Is your transaction_id unique?
If that is the case then you could perhaps use BEFORE UPDATE instead of AFTER UPDATE:
CREATE OR REPLACE TRIGGER tri1
BEFORE UPDATE
ON tab1
FOR EACH ROW
WHEN (NEW.col1 = 'YES')
BEGIN
   :NEW.col2 := 1;
END;If your transaction_id is not unique - so you really want to update more than one row in tab1 - your update cannot update the same row as the trigger reacted upon, even with the use of autonomous transaction. Then you could combine the above BEFORE UPDATE trigger with your own AFTER UPDATE, but then add ROWID != :OLD.ROWID to the where clause, but it would be a bad idea because some of your rows will be updated in one transaction and others in another transaction.
In general autonomous transaction is not a great way to solve mutating table problem in a trigger. Hopefully you have a unique transaction_id and can do BEFORE UPDATE - if not then a better way is to save the id's to be updated in a package array in the FOR EACH ROW triggers, and then do a AFTER UPDATE trigger that is NOT "for each row" to update the list of saved id's.