MySQL：ERROR 1064（42000）触发器

Question

有人可以帮我解决这个问题，请找出我做错了什么。

有时我没有这个错误......

CREATE DEFINER = CURRENT_USER TRIGGER `domitik_db`.`disp_hdw_BEFORE_INSERT`       BEFORE INSERT ON `disp_hdw` FOR EACH ROW
BEGIN

    declare boxId     int UNSIGNED;
    declare unitId    VARCHAR; 

    SET unitId=(SELECT homeunit FROM t_cpl WHERE t_cpl.id=NEW.idhardware);
    SET boxId=(SELECT dispositifs.idbox FROM dispositifs WHERE dispositifs.id = NEW.iddispositif);

IF (SELECT COUNT(*) FROM disp_hdw, dispositifs, t_cpl as tp WHERE disp_hdw.iddispositif = dispositifs.id AND disp_hdw.idhardware=tp.id AND dispositifs.idbox = boxId AND tp.homeunit=unitId > 0)
THEN 
    SIGNAL SQLSTATE '45000'
    SET MESSAGE_TEXT = 'Cannot add or update row: only one same homeunit id for a single box';
    END IF;

END;

第745行的错误1064（42000）：您的SQL语法出错;检查与您的MariaDB服务器版本对应的手册，以便在'附近使用正确的语法;

SET unitId =（SELECT homeunit FROM t_cpl WHERE t_cpl.id = NEW.idhardware）;