CREATE TRIGGER `before_insert_department_employee`
BEFORE INSERT ON `department_employee`
BEGIN
	IF new.employee_type = 'manager' AND EXISTS 
		(SELECT 'x' INTO count_managers FROM `department_employee` WHERE `department_id` = new.department_id AND `employee_id` = new.employee_id AND `employee_type` = new.employee_type)
		THEN
			SIGNAL SQLSTATE '23000'
			SET MESSAGE_TEXT = 'Trying to add duplicate manager';
	END IF;
END;

CREATE TRIGGER `before_insert_department_employee` 
BEFORE INSERT ON `department_employee`
BEGIN
	DECLARE count_managers int default 0;
	SELECT COUNT(*) INTO count_managers FROM `department_employee` WHERE `department_id` = new.department_id AND `employee_id` = new.employee_id AND `employee_type` = 'manager' AND `employee_type` = new.employee_type;
	IF count_managers > 0 THEN
		SIGNAL SQLSTATE '23000'
		SET MESSAGE_TEXT = 'Trying to add duplicate manager';
	END IF;
END;