Oracle Trigger PLS-00103. Query with multiple rows in temporal variable - sql

Question

I'm trying to write a trigger that raises error when someone attempts to rate a product which has not been bought. I have come up with a query to get the purchase history of a client :
SELECT nref
FROM CartClient a
INNER JOIN PaidCart b
ON a.idpurchase = b.idpurchase
INNER JOIN CartDetails c
ON b.idpurchase = c.idpurchase
WHERE a.Id = '12345672X'
which works fine.
So the next trigger should check if the product of a new rating (:new.NRef) has not been bought, namely is not part of the result of the last query (NOT IN).
CREATE OR REPLACE TRIGGER cant_rate
BEFORE INSERT ON Rating
FOR EACH ROW
BEGIN
IF (:new.NRef NOT IN (SELECT nref FROM CartClient a
INNER JOIN PaidCart b
ON a.idpurchase = b.idpurchase
INNER JOIN CartDetails c
ON b.idpurchase = c.idpurchase
WHERE a.Id =:new.Id)) THEN
RAISE_APPLICATION_ERROR(-20603,'Cant rate a not bought product');
END IF;
END;
I get error:
"PLS-00103:Encountered the symbol “INNER” when expecting one of".
I have tried to store the result of the query in a temporal variable using SELECT INTO. But, it's a multiple row result. What could I do?

Answer 1

How about such an approach?
CREATE OR REPLACE TRIGGER cant_rate
BEFORE INSERT ON Rating
FOR EACH ROW
DECLARE
l_exists NUMBER(1) := 0;
BEGIN
SELECT MAX(1)
INTO l_exists
FROM dual
WHERE EXISTS (SELECT nref FROM CartClient A
INNER JOIN PaidCart b
ON A.idpurchase = b.idpurchase
INNER JOIN CartDetails C
ON b.idpurchase = C.idpurchase
WHERE A.ID = :NEW.ID
AND a.nref = :NEW.nref --> is it "a.nref"?
);
IF l_exists = 0 THEN
RAISE_APPLICATION_ERROR(-20603,'Cant rate a not bought product');
END IF;
END;
Note remark "is it a.nref?" - you never said which table owns that nref column so I presumed it is cartclient; modify it, if necessary.
As of your attempt: if you executed it in SQL*Plus or SQL Developer, you'd see a message regarding subquery in IF; something like this:
LINE/COL ERROR
--------- -------------------------------------------------------------
2/3 PL/SQL: Statement ignored
2/21 PLS-00405: subquery not allowed in this context
So, no - you can't do it that way.

Answer 2

You probably don't get the actual error: PLS-00405 subquery not allowed in this context.
Simple stupid test:
BEGIN
IF 1 NOT IN ( SELECT 2 FROM DUAL )
THEN
NULL;
END IF;
END;
/
You can adjust your trigger in this way or similar:
CREATE OR REPLACE TRIGGER cant_rate
BEFORE INSERT ON Rating
FOR EACH ROW
DECLARE
l_test PLS_INTEGER;
BEGIN
SELECT CASE
WHEN :new.NRef NOT IN ( SELECT nref
FROM CartClient a
INNER JOIN PaidCart b
ON a.idpurchase = b.idpurchase
INNER JOIN CartDetails c
ON b.idpurchase = c.idpurchase
WHERE a.Id = :new.Id
)
THEN 1
ELSE 0
END
INTO l_test;
FROM DUAL;
IF l_test = 1
THEN
...
END IF;
END;
/