或: select * from tabA where aa in (select aa from tabB where x=1) and bb in (select bb from tabC where y=1)
select tabA.aa,tabA.bb from tabA where exists(select 1 from tabB where tabA.aa=tabb.aa and tabB.x=1) and exists(select 1 from tabC where tabA.bb=tabC.bb and tabC.y=1)
select * from tabA where aa in (select aa from tabB where x=1) and bb in (select bb from tabC where y=1)