mysql--(入门语句19--exit型子查询)

#exit型子查询

把外层的查询结果，拿到内层，看内层的查询是否成立.

select * from category;

select goods_id,cat_id,goods_name from goods;


#查有商品的栏目
select cat_id,cat_name from category where exits (select *from goods where goods.cat_id=category.cat_id);