OnMarch23manypeopletookpartin“Lights”activitytohelpsaveenergy.A．TurnoffB．ShowoffC．TakeoffD．Putoff
On March 23 many people took part in “_________ Lights” activity to help save energy.
A．Turn off B．Show off C．Take off D．Put off
A
设有关系R(A,B,C)和S(C,D)。与SQL语句Select A,B,D From R,S Wh 2020-05-23 …
设有关系R、S和T如下。关系T是由关系R和S经过______操作得到的。 R TA B C R.A 2020-05-24 …
A.πA,D(σC=D(R×S))B.πA,R,D(σS,C=R,D／(R×S))C.πA,R,D( 2020-05-26 …
A.πA,D(σC=D(R×S))B.πA,R.D(σR.C=S.D(R×S))C.πA,R.D(σ 2020-05-26 …
给定关系模式R(A.B,C,D)、S(C,D,E),与语句如下:A.A.C. S.C B.A.,B, 2020-05-26 …
A.B=软件工程OR R.C =S.C AND R.D =S.D B.B=‘软件工程‘ORRC =S 2020-05-26 …
SELECT (52)A.A,R.C,F,GB.A,C,S.B,S.FC.A,C,S.B,S.CD. 2020-05-26 …
(20)A.R.B = S.B AND R.C = S.C AND R.C < S.BB.R.B = 2020-05-26 …
(18)A.A, R.C, F, GB.A, C,S.B, S.FC.A, C, S.B,S.CD. 2020-05-26 …
A.πA,D(σC=D(R×S))B.πA,R.D(σS.C=R.D(R×S))C.πA,R.D(σ 2020-05-26 …