URGENT : Trigger

Question

Hi,
I'm trying to write a trigger on a Table ROOM_BLOCK to update a value in table ROOM_OOI_OOS.
As given below, which works perfectly.
BEGIN
IF INSERTING THEN
IF NVL(:NEW.ROOM_OOI_OOS_ID,0) <> 0 THEN
UPDATE ROOM_OOI_OOS SET NO_OF_ROOMS = NVL(NO_OF_ROOMS,0)+1
WHERE ROOM_OOI_OOS_ID = :NEW.ROOM_OOI_OOS_ID;
END IF;
ELSIF UPDATING THEN
IF NVL(:OLD.ROOM_OOI_OOS_ID,0) <> 0 THEN
UPDATE ROOM_OOI_OOS SET NO_OF_ROOMS = NVL(NO_OF_ROOMS,0)-1
WHERE ROOM_OOI_OOS_ID = :OLD.ROOM_OOI_OOS_ID;
END IF;
IF NVL(:NEW.ROOM_OOI_OOS_ID,0) <> 0 THEN
UPDATE ROOM_OOI_OOS SET NO_OF_ROOMS = NVL(NO_OF_ROOMS,0)+1
WHERE ROOM_OOI_OOS_ID = :NEW.ROOM_OOI_OOS_ID;
END IF;
ELSE
IF NVL(:OLD.ROOM_OOI_OOS_ID,0) <> 0 THEN
UPDATE ROOM_OOI_OOS SET NO_OF_ROOMS = NVL(NO_OF_ROOMS,0)-1
WHERE ROOM_OOI_OOS_ID = :OLD.ROOM_OOI_OOS_ID;
END IF;
END IF;
END;
But when I add a select statement. the trigger seems to fail with a mutating error ORA-04091
and Error at Line which executes the statement immidiate ORA-04088.
DECLARE
stmt VARCHAR2(500);
vcount INTEGER;
BEGIN
IF INSERTING THEN
--INSERT INTO SHRUTI_TEST (DESCR) VALUES ('Inserting');
IF NVL(:NEW.ROOM_OOI_OOS_ID,0) <> 0 THEN
stmt := 'Select count(*) from ROOM_BLOCK ' ||
' WHERE ROOM_OOI_OOS_ID = ' || :NEW.ROOM_OOI_OOS_ID ||
' AND ROOM_NO = ''' || :NEW.ROOM_NO || ''' ';
EXECUTE IMMEDIATE stmt INTO vcount;
IF vcount = 1 THEN
UPDATE ROOM_OOI_OOS SET NO_OF_ROOMS = NVL(NO_OF_ROOMS,0)+1
WHERE ROOM_OOI_OOS_ID = :NEW.ROOM_OOI_OOS_ID;
END IF;
END IF;
ELSIF UPDATING THEN
IF NVL(:OLD.ROOM_OOI_OOS_ID,0) <> 0 THEN
UPDATE ROOM_OOI_OOS SET NO_OF_ROOMS = NVL(NO_OF_ROOMS,0)-1
WHERE ROOM_OOI_OOS_ID = :OLD.ROOM_OOI_OOS_ID;
END IF;
IF NVL(:NEW.ROOM_OOI_OOS_ID,0) <> 0 THEN
UPDATE ROOM_OOI_OOS SET NO_OF_ROOMS = NVL(NO_OF_ROOMS,0)+1
WHERE ROOM_OOI_OOS_ID = :NEW.ROOM_OOI_OOS_ID;
END IF;
ELSE
IF NVL(:OLD.ROOM_OOI_OOS_ID,0) <> 0 THEN
UPDATE ROOM_OOI_OOS SET NO_OF_ROOMS = NVL(NO_OF_ROOMS,0)-1
WHERE ROOM_OOI_OOS_ID = :OLD.ROOM_OOI_OOS_ID;
END IF;
END IF;
END;
Please tell me how to solve this problem...
Regards
Mike.

Answer 1

Read the following link.
http://asktom.oracle.com/~tkyte/Mutate/index.html