A．AB
B．ABC
C．ABD
D．ABE
(B) (A BA)=r(A).-|||-(C) (A B)=max r(A), r(B)). (D) (A B)=r((A)^T (B)^T).
[单选题]Consider the following information in relation to a portfolio composed of F
[单选题]有关系R(A,B,C,D) 和关系S(A,B,C,D,E,F)，关系T是R与S的笛卡尔积，即T=R×S。则关系T的属性个数是( )。A．4B．6C．10D．24
,(x)_(n))}^T 且 ^TAx=(x)^TBx, 则 A=B 的充要条-|||-件是 ()-|||-(A) (A)=R(B); (B) ^T=A;-||
[单选题]Let R and S be the relation respection respectively：Relation R:A B C Relation S:B C D1 2 3 2 3 46 7 8 2 3 59 7 8 7 8 1The number of tuples that the result of the expression R∞S(Here if natural join of relations R and S) is (69) ．(69) A．1B．4C．7D．10
[单选题]Let R and S be the relation respectively: Relation R: A B C Relation S: B C D 1 2 3 2 3 4 6 7 8 2 3 5 The number of tuplesthat the result of the expression R ∞ S (Here is the natural join of relations R and S) isA．3B．4C．6D．9
10,有三个关系R S和T如下:则关系T是由关系R和S通过某种操作得到,该操作为()。T S R A A B C A B C a 1 2 d 3 2 a 1 2
[单选题]F．or relation R where primary key contains multiple, no non-key attribute should be functionally dependent on a part of the primary key.This relation R is at least inA．1NFB．2NFC．3NFD．BCNF
[单选题]Suppose we have the relation schema R(A,B,C,D)with functional dependencies;F{A→B,B→C,C→D,D→A},then R(A,B,C,D)at least is inA．1NFB．2NFC．3NFD．BCNF
[单选题]F．or relation R where primary key contains multiple attributes,no non-key attribute should be functionally dependent on a part of the primary key. This relation R is at least inA． 1NFB．2NFC．3NFD．BCNF