exists,not exists,in

1、exists子查询的功能是判断返回结果中是否有数据行

SELECT DISTINCT goods_name FROM goods WHERE EXISTS (SELECT * FROM brand WHERE cat_id = goods.cat_id AND name='索尼');

2、in查询数据是否有匹配的

SELECT DISTINCT goods_name FROM goods WHERE cat_id IN(SELECT cat_id  FROM brand WHERE cat_id = goods.cat_id AND name='索尼');