PL/SQL Oracle Mutant table-how to encounter this issue plz? - sql

Question

th request is to assure that in the city we have only one branch,
Banch (idBranch(PK), city) for update and insert
the idea I got is to create a temporary table having all the data of the first one so i can escape the ora errors this is the code I wrote, i'm facing the error PL/SQL: ORA-00903 and I'm not so sure if one trigger can do he job in this case since it should be working for inserting and updating. I need your advice please, thank you.
` CREATE TABLE TEMP_BRANCH AS SELECT NumBranch, CITY FROM BRANCH;
CREATE OR REPLACE TRIGGER checkUniqueBranchPerCity
BEFORE INSERT OR UPDATE ON BRANCH
REFERENCING
NEW AS nextLine
FOR EACH ROW
BEGIN
LOCK TABLE TEMP_BRANCH IN ROW SHARE MODE;
FOR line IN (SELECT * FROM TEMP_BRANCH) LOOP
IF :nextLine.City = line.City THEN
RAISE_APPLICATION_ERROR;
END IF;
END LOOP;
DELETE * FROM TEMP_BRANCH;
END;
/ `

Answer 1

ORA-00903 is "Invalid table name". I suspect it's caused because you put a colon in front of nextLine, i.e. you wrote
IF :nextLine.City = line.City THEN
when it should be
IF nextLine.City = line.City THEN
But I suggest getting rid of the REFERENCING clause and just using :NEW and :OLD in triggers as it reduces confusion. So use
CREATE TABLE TEMP_BRANCH AS SELECT NumBranch, CITY FROM BRANCH;
CREATE OR REPLACE TRIGGER checkUniqueBranchPerCity
BEFORE INSERT OR UPDATE ON BRANCH
FOR EACH ROW
BEGIN
LOCK TABLE TEMP_BRANCH IN ROW SHARE MODE;
FOR line IN (SELECT * FROM TEMP_BRANCH) LOOP
IF :NEW.City = line.City THEN
RAISE_APPLICATION_ERROR;
END IF;
END LOOP;
END;
/
I also suggest you get rid of the DELETE statement in the trigger as it will delete the contents of TEMP_BRANCH the first time the trigger fires.