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(2<7(R??S))等价的SQLSELECT()FROMR,SWHERE(作答此空) A.R. B, D, F,G B.R. B, E,S. C, F,G C.R. B,R. D,S. C,F
A.R. B.R. C.S. D.F正确答案A
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(2<7(R??S))等价的SQLSELECT()FROMR,SWHERE(作答此空) A.R. B, D, F,G B.R. B, E,S. C, F,G C.R. B,R. D,S. C,F
A.R. B.R. C.S. D.F正确答案A