PL/SQL Ttrigger select data from 2 tables with the same row - plsql

Question

i have a probelm with a little project.
I have these tables:
USER (TAG VARCHAR, NICKNAME VARCHAR, TAG_CLAN VARCHAR)
DONATION(DATE_DON DATE, DON_SEND VARCHAR, DON_REIC VARCHAR)
THE ELEMENTS: DON_SEND AND DON_REICV ARE THE FOREIGN KEY THAT POINTS TO THE MANI (TAG) OF THE TABLE USER.
I'm trying to make a trigger that allows users to make and receive donations only if the TAG_CLAN is the same
I tried in this way but it doesn't work:
CREATE OR REPLACE TRIGGER CONTROLLO_USER_DONAZIONE
BEFORE INSERT ON DONAZIONE
FOR EACH ROW
DECLARE
TAG_C1 UTENTE.NUM_CLAN%TYPE;
TAG_C2 UTENTE.NUM_CLAN%TYPE;
CLAN_DIFF EXCEPTION;
BEGIN
SELECT U.NUM_CLAN INTO TAG_C1
FROM DONAZIONE D JOIN UTENTE U ON D.COD_UTENTE_EFFETTUA=U.TAG_USER
WHERE D.COD_UTENTE_EFFETTUA=(:NEW.COD_UTENTE_EFFETTUA);
SELECT U.NUM_CLAN INTO TAG_C2
FROM DONAZIONE D JOIN UTENTE U ON D.COD_UTENTE_RICEVE=U.TAG_USER
WHERE D.COD_UTENTE_RICEVE=(:NEW.COD_UTENTE_RICEVE);
IF TAG_C1<>TAG_C2 THEN
RAISE CLAN_DIFF;
END IF;
EXCEPTION
WHEN CLAN_DIFF THEN
RAISE_APPLICATION_ERROR(-20003,'NON SIETE NELLO STESSO CLAN, QUINDI NON PUOI RICEVERE/DONARE CARTE!');
END;
Can you help me please?

Answer 1

There are some differences between the tables you posted and the code of your trigger. With tables like these:
CREATE TABLE utente
(
TAG_USER VARCHAR2(10) PRIMARY KEY,
NICKNAME VARCHAR2(10),
NUM_CLAN VARCHAR2(10)
);
CREATE TABLE DONAZIONE
(
DATE_DON DATE,
COD_UTENTE_EFFETTUA VARCHAR2(10) REFERENCES utente(TAG_USER),
COD_UTENTE_RICEVE VARCHAR2(10) REFERENCES utente(TAG_USER)
);
This could be your trigger:
CREATE OR REPLACE TRIGGER CONTROLLO_USER_DONAZIONE
BEFORE INSERT
ON DONAZIONE
FOR EACH ROW
DECLARE
TAG_C1 UTENTE.NUM_CLAN%TYPE;
TAG_C2 UTENTE.NUM_CLAN%TYPE;
CLAN_DIFF EXCEPTION;
BEGIN
SELECT U.NUM_CLAN
INTO TAG_C1
FROM UTENTE U
WHERE U.TAG_USER = :NEW.COD_UTENTE_EFFETTUA;
SELECT U.NUM_CLAN
INTO TAG_C2
FROM UTENTE U
WHERE U.TAG_USER = :NEW.COD_UTENTE_RICEVE;
IF TAG_C1 <> TAG_C2
THEN
RAISE CLAN_DIFF;
END IF;
EXCEPTION
WHEN CLAN_DIFF
THEN
RAISE_APPLICATION_ERROR(-20003, 'NON SIETE NELLO STESSO CLAN, QUINDI NON PUOI RICEVERE/DONARE CARTE!');
END;
With data like the following:
insert into utente(TAG_USER, NICKNAME, NUM_CLAN) values ('one', 'User one', 'Numbers');
insert into utente(TAG_USER, NICKNAME, NUM_CLAN) values ('two', 'User two', 'Numbers');
insert into utente(TAG_USER, NICKNAME, NUM_CLAN) values ('a', 'User a', 'Letters');
it works like:
SQL> insert into donazione(DATE_DON, COD_UTENTE_EFFETTUA, COD_UTENTE_RICEVE) values (sysdate, 'one', 'two');
1 row created.
SQL> insert into donazione(DATE_DON, COD_UTENTE_EFFETTUA, COD_UTENTE_RICEVE) values (sysdate, 'a', 'two');
insert into donazione(DATE_DON, COD_UTENTE_EFFETTUA, COD_UTENTE_RICEVE) values (sysdate, 'a', 'two')
*
ERROR at line 1:
ORA-20003: NON SIETE NELLO STESSO CLAN, QUINDI NON PUOI RICEVERE/DONARE CARTE!
ORA-06512: at "ALEK.CONTROLLO_USER_DONAZIONE", line 23
ORA-04088: error during execution of trigger 'ALEK.CONTROLLO_USER_DONAZIONE'
The issue in your code is that you do a join, assuming that the record you're inserting already exists in the table DONAZIONE, this getting a no_data_found exception.
As an aside, I changed varchar into varchar2; have a look at the difference between them.
Also, this assumes that NUM_CLAN always is NOT NULL.
EDIT:
Given the way you need to handle null values, you can edit the IF
IF TAG_C1 <> TAG_C2
into
IF TAG_C1 <> TAG_C2 or TAG_C1 is null or TAG_C2 is null
or, more compact, but less readable:
IF nvl(TAG_C1, 'a value that a clan can never have') <> nvl(TAG_C2 , 'some other impossible value')