book_room | 实现了两套平台的预定系统，包括客户使用的前台系统和员工使用的后台系统 | Frontend Framework library

CREATE TRIGGER ins_meal_details
AFTER INSERT 
ON meal_details
FOR EACH ROW 
INSERT INTO sql_changes (sc_table, 
                         sc_reason,
                         sc_key,
                         sc_value, 
                         sc_done)
SELECT 'book_room',
       'DINNER1',
       CONCAT('bh_no=',NEW.bh_no,',date=',NEW.md_date),
       1, 
       0
WHERE NOT EXISTS (SELECT 1 
                  FROM booking 
                  WHERE bh_no = NEW.bh_no 
                    AND bo_date = NEW.md_date 
                    AND bo_meals < 1);