SQL exist

EXISTS = IN,意思相同不过语法上有点点区别，好像使用IN效率要差点，应该是不会执行索引的原因
SELECT ID,NAME FROM A　 WHERE　ID IN (SELECT AID FROM B)

NOT EXISTS = NOT IN ,意思相同不过语法上有点点区别
SELECT ID,NAME FROM A WHERE　ID　NOT IN (SELECT AID FROM B)