--A表大，B表小，用A表的索引，B表会被全扫描，效率高
select * from A where ID in (select ID from B)

--A表小，B表大，用B表的索引，A表会被全扫描，效率高
select * from A as TA where exists(select 1 from B as TB where TB.ID = TA.ID)

--not in 全表扫描
--not exists 会用到索引