Need help writing a TRIGGER !!!

Question

The trigger below:
create or replace
TRIGGER dtworepair_after_update_status
AFTER UPDATE OF worepair_status
ON dtworepair
FOR EACH ROW
WHEN (NEW.worepair_status = 'CLOSED')
DECLARE
--workorder_nbr_var   dtworepair.worepair_wonbr%TYPE;*
id_count_var        NUMBER;
status_count_var    NUMBER;
BEGIN
SELECT COUNT(worepair_wonbr) INTO id_count_var
FROM dtworepair
WHERE worepair_wonbr = :OLD.worepair_wonbr;
SELECT COUNT(worepair_status) INTO status_count_var
FROM dtworepair
WHERE worepair_status = 'CLOSED' AND worepair_wonbr = :OLD.worepair_wonbr;
IF UPDATING THEN
IF id_count_var != status_count_var THEN
update_wo_status_proc(:OLD.worepair_wonbr,'OPEN');
ELSIF id_count_var = status_count_var THEN
update_wo_status_proc(:OLD.worepair_wonbr,'CLOSED');
END IF;
END IF;
END dtworepair_after_update_status;
is suppose to fire when the DTWORepair table worepair_status column is updated to 'CLOSED'. And if all the records with the same worepair_wonbr now have a 'CLOSED' worepair_status then this trigger is suppose to call the procedure:
create or replace
PROCEDURE update_wo_status_proc
repair_wonbr_param  IN dtworkorder.wo_nbr%TYPE,
status_param        IN VARCHAR2
AS
BEGIN
IF status_param = 'CLOSED' OR status_param = 'OPEN' THEN
UPDATE dtworkorder
SET wo_status = status_param, wo_enddate = SYSDATE
WHERE wo_nbr = repair_wonbr_param;
END IF;
END update_wo_status_proc;
But I keep getting the error below when I try:
UPDATE dtworepair
SET worepair_status = 'CLOSED'
WHERE worepair_wonbr = 2 AND worepair_tasknbr = 4;
Error starting at line 1 in command:
UPDATE dtworepair
SET worepair_status = 'CLOSED'
WHERE worepair_wonbr = 2 AND worepair_tasknbr = 4
Error report:
SQL Error: ORA-04091: table DISTRAN.DTWOREPAIR is mutating, trigger/function may not see it
ORA-06512: at "DISTRAN.DTWOREPAIR_AFTER_UPDATE_STATUS", line 6
ORA-04088: error during execution of trigger 'DISTRAN.DTWOREPAIR_AFTER_UPDATE_STATUS'
04091. 00000 - "table %s.%s is mutating, trigger/function may not see it"
*Cause:    A trigger (or a user defined plsql function that is referenced in
this statement) attempted to look at (or modify) a table that was
in the middle of being modified by the statement which fired it.
*Action:   Rewrite the trigger (or function) so it does not read that table.
worepair_wonbr worepair_tasknbr worepair_id worepair_status worepair_labor
1     1     15     CLOSED     0.5
2     1     3     CLOSED     0.75
2     2     4     CLOSED     2
2     3     5     CLOSED     0.25
2     4     6     OPEN     0.5
For example, worepair_wonbr 2 in the above table has 1 record in the DTWorkorder table and 4 worepair_tasknbr in the above table. So long as 1 of the task,worepair_status, in the above table is OPEN, then the trigger will not fire. The Trigger should only fire when all 4 worepair_status in the above table for worepair_wonbr 2 are 'CLOSED'. This should in-turn run the procedure that will change the wo_status in DTWorkorder table to 'CLOSED' for wo_nbr 2.
This is in a nutshell what I am trying to accomplish.
Any ideas?

Answer 1

Hi,
'mutating trigger' error means that you are trying to use a trigger on a table to modify the contents of the same table -- Oracle doesn't allow that.
The standard workaround for this problem is to use row-level triggers to fill an array with data of rows that need to be modified, and do the modification in the statement-level trigger.
From 11g on, you can use compound triggers to do all in one trigger, see example in:
http://www.oracle-base.com/articles/11g/TriggerEnhancements_11gR1.php
Best regards,
Nikolay