给定关系R(A,B,C,D,E)与S(B,C,F,G),那么与表达式π2,4,6,7(σ2<7(R??S))等价的SQL语句如下:
SELECT(41)FROMR,SWHERE(42);
41、A.R.B,D,F,G
B.R.B,E,S.C,F,G
C.R.B,R.D,S.C,F
D.R.B,R.C,S.C,F
42、A.R.B=S.BORR.C=S.CORR.B<S.G
B.R.B=S.BORR.C=S.CORR.B<S.C
C.R.B=S.BANDR.C=S.BANDR.B<S.G
D.R.B=S.BANDR.C=S.BANDR.B<S.C