mysql--(入門語句19--exit型子查詢)

#exit型子查詢 把外層的查詢結果，拿到內層，看內層的查詢是否成立. select * from category; select goods_id,cat_id,goods_name from goods;#查有商品的欄目select cat_id,cat_name from category where exits (select *from goods where goods.cat_id

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