Help on delete trigger

Question

Hi all,
I have a situation like this
I have a table like
SQL> desc system_user
Name Null? Type
ID NOT NULL NUMBER(12)
USER_ID NOT NULL VARCHAR2(30)
SQL> SELECT * FROM SYSTEM_USER
2 ORDER BY CTUT_ID;
CTUT_ID CURRENT_USER_ID
1 KTYLOR
2 EXAMPLE
3 SCOTT
SQL> DESC ALL_USERS;
Name Null? Type
USERNAME NOT NULL VARCHAR2(30)
USER_ID NOT NULL NUMBER
CREATED NOT NULL DATE
What i need to do is i need to have before delete trigger to check the following condition when user try to delete a record in table
SYSTEM_USER
1) suppose user is trying to delete a record "SCOTT" IN TABLE
SYSTEM_USER
CONDITION SHOULD CHECK THAT IF USER_NAME EXITS IN TABLE "ALL_USER"
1)IF HE EXITS THEN RAISE ERROR
2)IF HE IS NOT EXITS THEN DELETE THE RECORD IN TABLE "SYSTEM_USER"
SO I WROTE A CODE FOR TRIGGER
SQL> CREATE OR REPLACE TRIGGER TIBD_USER
2 BEFORE DELETE ON SYSTEM_USER FOR EACH ROW
3 DECLARE
4 FOUND_USER NUMBER(2);
5 BEGIN
6 SELECT COUNT(*) FROM ALL_USERS
7 WHERE USERNAME = :OLD.USER_ID;
8 IF FOUND_USER = 0 THEN
9 DELETE FROM SYSTEM_USER
10 WHERE ROWID := :NEW.ROWID;
11 ELSE
12 RAISE_APPLICATION_ERROR(-20000,'USER FOUND IN ALL_USERS TABLE');
13 END IF;
14 END TIBD_USER;
15 /
Warning: Trigger created with compilation errors.
SQL> SHOW ERRORS
Errors for TRIGGER TIBD_USER:
LINE/COL ERROR
7/1 PL/SQL: SQL Statement ignored
8/13 PL/SQL: ORA-00920: invalid relational operator
ANY HELP PLEASE

Answer 1

1 CREATE OR REPLACE TRIGGER TIBD_USER
2 BEFORE DELETE ON SYSTEM_USER FOR EACH ROW
3 DECLARE
4 FOUND_USER NUMBER(2);
5 BEGIN
6 SELECT COUNT(*) INTO FOUND_USER FROM ALL_USERS
7 WHERE USERNAME = :OLD.USER_ID;
8 IF FOUND_USER = 0 THEN
9 DELETE FROM SYSTEM_USER
10 WHERE ROWID = :OLD.ROWID;
11 ELSE
12 RAISE_APPLICATION_ERROR(-20000,'USER FOUND IN ALL_USERS TABLE');
13 END IF;
14* END TIBD_USER;
SQL> /
Trigger created.
WHEN I DELETE A RECORD IT IS GIVING ME THAT
SQL> DELETE FROM SYSTEM_USER
2 WHERE CTUT_ID = 3;
DELETE FROM SYSTEM_USER
ERROR at line 1:
ORA-04091: table SYSTEM_USER is mutating, trigger/function may not see it
ORA-06512: at "TIBD_USER", line 7
ORA-04088: error during execution of trigger 'TIBD_USER'