我试图创建一些触发器为我的web数据库，但没有工作代码为我的触发器在这里的问题

BEGIN
DECLARE t INT;
DECLARE b INT;
DECLARE ir INT;
DECLARE tgl INT;
DECLARE kol VARCHAR(3);


SET tgl = "(SELECT RIGHT(booking_checkin, 2) FROM pt_bookings WHERE booking_id = NEW.booking.id)";

SET ir = "(SELECT booked_room_id FROM pt_booked_rooms WHERE booking_id = NEW.booking.id)";

SET b = "(SELECT MID(booking_checkin , 6,2) FROM pt_bookings WHERE booking_id = NEW.booking_id)";

SET t = "SELECT IF((SELECT LEFT(booking_checkin, 4) FROM pt_bookings WHERE booking_id = NEW.booking_id) = 2019 ,'0','1')";

SET kol = "d" + tgl;

UPDATE pt_rooms_availabilities
set kol = kol + (SELECT `booking_nights` FROM `pt_bookings` WHERE booking_id = NEW.booking_id)
WHERE room_id = ir AND y = t AND m= b; 
END

问题是var kol不读作为一个列的名称，也许有人可以帮助我？