Checking if every table object has a different name - oracle

Question

I have a Users table, each User has a identifier, a name and some other fields.
I need to check if there is another user with the same name after inserting or updating, so I made this trigger:
CREATE OR REPLACE TRIGGER user_name
BEFORE
INSERT OR UPDATE
ON Users
FOR EACH ROW
DECLARE
count INTEGER;
BEGIN
SELECT COUNT(*) INTO count FROM Users WHERE name = :new.name AND idUser <> :new.idUser;
IF count > 0
THEN raise_application_error(-20007, 'There is already another user with the same name');
END IF;
END;
It seems to work when inserting new users, but it doesn't when I update them, it looks like it "ignores" the idUser check so it always fails as it finds the same user with the same name.
Why is this happening? Thank you

Answer 1

In triggers , there are 3 states as you know inserts update and delete , In update states there are new values and old values , I mean when you update a column you , you will replace the old value with new one , in trigger you can use the old and the new value of the column .. Please check this example
CREATE or REPLACE TRIGGER test001
AFTER INSERT OR UPDATE OR DELETE ON tabletest001
DECLARE
Operation NUMBER;
CustomerCode CHAR(10 BYTE);
BEGIN
IF INSERTING THEN
Operation := 1;
CustomerCode := :new.field1;
END IF;
IF UPDATING THEN
Operation := 2;
CustomerCode := :old.field1;
END IF;
// DO SOMETHING ...
EXCEPTION
WHEN OTHERS THEN ErrorCode := SQLCODE;
END;
/
in the above example , in update state I used old.value of the column , so in your example you should check the old value not new , please try it
if updating then
SELECT COUNT(*) INTO count FROM Users WHERE name = :old.name AND idUser <> :old.idUser;
IF count > 0
THEN raise_application_error(-20007, 'There is already another user with the same name');
end if
however as in the comments adviced you is to use primary key, however my answer is to give you understanding to triggers