product(maker,model,type)
pc(model,speed,ram,hd,price)
laptop(model,speed,ram,hd,screen,price)
printer(model,color,type,price)
题目是删除所有不生产打印机的厂商生产的笔记本电脑。。
我写的语句是
delete from product
where maker not in(select maker from product where type='printer')
and type='laptop';
求指导
pc(model,speed,ram,hd,price)
laptop(model,speed,ram,hd,screen,price)
printer(model,color,type,price)
题目是删除所有不生产打印机的厂商生产的笔记本电脑。。
我写的语句是
delete from product
where maker not in(select maker from product where type='printer')
and type='laptop';
求指导
on a.maker=b.maker
where b.type='printer' and a.type='laptop';
where a.type='laptop' and b.maker is Null;