DROP TRIGGER `members_before_insert`; CREATE DEFINER=`neo`@`%` TRIGGER `members_before_insert` BEFORE INSERT ON `members` FOR EACH ROW BEGIN IF new.username IS NOT NULL THEN IF not exists(select username from members_available where username = new.username) THEN /*set new.username = NULL;*/ SIGNAL SQLSTATE '45000' SET MESSAGE_TEXT = 'An error occurred', MYSQL_ERRNO = 1001; END IF; END IF; END;