Problem with a trigger

Question

I have a problem with a very simple trigger:
CREATE OR REPLACE TRIGGER contratos_factuali
AFTER UPDATE OF descrip,fautori,origpeso,origdls,
montopeso,montodls,aant,aact,fifiobserva,pedsap
ON ulises.contratos
FOR EACH ROW
BEGIN
UPDATE contratos SET factuali=TO_DATE(SYSDATE,'DD/MM/YYYY HH24:MI')
WHERE ncontra=:NEW.ncontra;
COMMIT;
END;This trigger update the column 'factuali' of this table everytime any other column of this table is updated. But returns me an error:
SQL> update contratos set montodls=1 where ncontra='ODPS-086/00';
update contratos set montodls=1 where ncontra='ODPS-086/00'
ERROR at line 1:
ORA-04091: table ULISES.CONTRATOS is mutating, trigger/function may not see it
ORA-06512: at "ULISES.CONTRATOS_FACTUALI", line 2
ORA-04088: error during execution of trigger 'ULISES.CONTRATOS_FACTUALI'What's happening?

Answer 1

(1) You cannot use DML to update the table on which the trigger is based. Think about it: your trigger fires on UPDATE so each time fires, it updates the table and fires again. This is what is known as mutation.
What you should do is create a trigger that executes BEFORE the update and simply do
:NEW.factuali := SYSDATE;
If ncontra is not a unique column and you genuinely want all rows of the same value to have the same factuali timestamp, well, it's very difficult, indeed I don't think it can be done. You could try submitting a DBMS_JOB to do the update, passing in the factuali value as a parameter; that DBMS_JOB would have to disable the trigger before doing the update (to prevent the recursion) and then re-enable it afterwards. Which seems like a lot of work: are you sure your design is correct?
(2) You don't need the commit statement: the triggere exectutes within the commit phase of the original update.
HTH, APC