表字段
商品表： goods（gid，gname，price）其屬性是商品編碼，商品名稱，單價
銷售表： detail （did，gid，price，shuliang，jine）其屬性是銷售單號，商品編號，單價，數量，金額
添加商品，自動向銷售明細裏添加數據
DELIMITER $$
DROP TRIGGER IF EXISTS ins_detail_on_goods $$
CREATE TRIGGER ins_detail_on_goods
AFTER INSERT ON goods
FOR EACH ROW BEGIN
INSERT detail(gid,price,shuliang,jine) VALUES(new.gid,new.price,0,0);
END$$刪除商品，自動刪除銷售明細裏的數據
DELIMITER $$
DROP TRIGGER IF EXISTS del_detail_on_goods $$
CREATE TRIGGER del_detail_on_goods
AFTER DELETE ON goods
FOR EACH ROW BEGIN
DELETE FROM detail WHERE gid=old.gid;
END$$修改商品的單價，自動修改銷售明細裏對應商品的單價和金額
DELIMITER $$
DROP TRIGGER IF EXISTS upd_detail_on_goods $$
CREATE TRIGGER upd_detail_on_goods
AFTER UPDATE ON goods
FOR EACH ROW BEGIN
UPDATE detail SET price=new.price,jine=shuliang*(new.price) WHERE gid=(SELECT gid FROM goods WHERE price=new.price);
END$$