exists指令

• 看看是不是存在有資料，後面刮號中的查詢有回傳資料才算是true，否則就是false

select cid,model ,price from car where

exists (

select 1 from sale where sale.cid=car.cid

);

select cid,model ,price from car where

not exists (

select 1 from sale where sale.cid=car.cid

);