How to check if table exists in MySql db?

MySQL Trigger check if value exists in table of another DB

• I need to create a trigger that before insert will check if the username that's trying to be added, already exists (case sensitive) in the table of another database (same mysql server). This is what I have so far: CREATE TRIGGER trig_user_insert BEFORE INSERT ON users FOR EACH ROW BEGIN IF ( ) THEN SIGNAL SQLSTATE '45000' SET MESSAGE_TEXT = 'Error message'; END IF; END So, how can I make that only if it exists in the table of the other database then insert the row. and is there any better way to stop the insert other than SIGNAL?

• Answer:

  Try: CREATE TRIGGER tg_bi_users BEFORE INSERT ON users FOR EACH ROW SET NEW.user = IF(EXISTS ( SELECT * FROM othertable WHERE user IN(NEW.user) ), NULL, NEW.user);