Compile error on if else condition in trigger - oracle

Question

create or replace
TRIGGER TRG_DEPT_ID BEFORE INSERT ON DEPT FOR EACH ROW
BEGIN
IF NOT EXISTS (SELECT * FROM DEPT cd WHERE cd.st_num = :new.ST_NUMBER AND cd.td_NUMBER = :new.TD_NUMBER)
THEN
SELECT SEQ_DEPT_ID.NEXTVAL INTO :new.ID FROM dual;
ELSE
SELECT ID FROM DEPT INTO :new.ID WHERE cd.st_num = :new.ST_NUMBER AND cd.td_NUMBER = :new.TD_NUMBER;
END IF;
END ;
I am trying to check for duplicate entry. If not exists, then I will create a new Id from sequence. Else I will put the same id.
And the SaveOrUpdate(dept); will do the remaining.
But it gave me compile error.Error(8,9): PL/SQL: SQL Statement ignored.
UPDATE:
When I tried the following query:
CREATE OR REPLACE TRIGGER TRG_DEPT_ID
BEFORE INSERT ON DEPT FOR EACH ROW
BEGIN
BEGIN
SELECT ID
INTO :NEW.ID
FROM DEPT
WHERE cd.st_num = :NEW.ST_NUMBER
AND cd.td_NUMBER = :NEW.TD_NUMBER;
EXCEPTION WHEN no_data_found THEN
SELECT SEQ_DEPT_ID.NEXTVAL INTO :new.ID FROM dual;
END;
END;
Getting the error:
ORA-01422: exact fetch returns more than requested number of rows
How to handle this error?

Answer 1

You can simply code your trigger like this,
CREATE OR REPLACE TRIGGER TRG_DEPT_ID
BEFORE INSERT ON DEPT FOR EACH ROW
BEGIN
BEGIN
SELECT ID
INTO :NEW.ID
FROM DEPT
WHERE cd.st_num = :NEW.ST_NUMBER
AND cd.td_NUMBER = :NEW.TD_NUMBER
AND rownum = 1; --Use rownum = 1 to avoid selecting too many rows.
EXCEPTION WHEN no_data_found THEN
SELECT SEQ_DEPT_ID.NEXTVAL INTO :new.ID FROM dual;
--:NEW.id = seq_dept_id.nextval; -- Or you can use this if you are using 11g or higher versions.
END;
END;
Edited:
You can modify your trigger code as below if duplicate entries are there in your table.
CREATE OR REPLACE TRIGGER TRG_DEPT_ID
BEFORE INSERT ON DEPT FOR EACH ROW
DECLARE
l_id DEPT.id%type;
BEGIN
BEGIN
SELECT ID
INTO l_id
FROM DEPT
WHERE cd.st_num = :NEW.ST_NUMBER
AND cd.td_NUMBER = :NEW.TD_NUMBER
AND ROWNUM = 1; --Use rownum = 1 to avoid selecting too many rows.
IF l_id IS NOT NULL THEN --If same st_number and td_number exists.
raise_application_error( -20001, 'Duplicate entry.');
END IF;
EXCEPTION WHEN no_data_found THEN
SELECT SEQ_DEPT_ID.NEXTVAL INTO :new.ID FROM dual;
--:NEW.id = seq_dept_id.nextval; -- Or you can use this if you are using 11g or higher versions.
END;
END;

Answer 2

try adding rownum in the where section :
CREATE OR REPLACE TRIGGER TRG_DEPT_ID
BEFORE INSERT ON DEPT FOR EACH ROW
BEGIN
BEGIN
SELECT ID
INTO :NEW.ID
FROM DEPT
WHERE cd.st_num = :NEW.ST_NUMBER
AND cd.td_NUMBER = :NEW.TD_NUMBER
AND ROWNUM =1;
EXCEPTION WHEN no_data_found THEN
SELECT SEQ_DEPT_ID.NEXTVAL INTO :new.ID FROM dual;
END;
END;
That will make the query to just return 1 row in case cd.st_num and cd.td_NUMBER are repeated in more than one row.
On the other hand, if you need to detect that there are more than one row for these two columns , you can catch the exception TOO_MANY_ROWS in the exceptions section
EXCEPTION WHEN no_data_found THEN
SELECT SEQ_DEPT_ID.NEXTVAL INTO :new.ID FROM dual;
when TOO_MANY_ROWS then
-- your logic to do when there are too many rows
END;