G select * from t1 where f1 in (select f1 from t2); (before rewrites) cluster0 Box0:Select cluster2 Box2:Select cluster3 Box3:BaseTable T2 cluster1 Box1:BaseTable T1 boxhead0 Distinct: Preserve 0: Q0.c0 as F1 1: Q0.c1 as F2 2: Q0.c2 as F3 Q0 Q0(F) as T1 Q2 Q2(E) Q0->Q2 (Q0.c0) = (Q2.c0) boxhead1 Distinct: Preserve 0: c0 as F1 1: c1 as F2 2: c2 as F3 Q0->boxhead1 boxhead2 Distinct: Preserve 0: Q1.c0 as F1 Q2->boxhead2 Q1 Q1(F) as T2 boxhead3 Distinct: Preserve 0: c0 as F1 1: c1 as F2 2: c2 as F3 Q1->boxhead3