A select *from t1, t2 where t1.a=t2.a
B select t1.*, t2.*from t1 inner join t2 on t1.a=t2.a.a
C select t1.*, t2.*from t1, t2where t1.a in t2.a and t2.a in t1.a
D select t1.*, t2.*from t1, (select * from t2) t2where t2.a=t1.a
E select *from (select * from t1) x,(select * from t2) ywhere x.a=y.a