3 3 votes Consider the following relation: R (A1, A,2, ....., An) and Every (n – 2) attributes of R forms Candidate key. Which of the following represents the number of super keys are there in R ? a. nCn–2 * 22 b. nCn–2 + n + 1 c. nCn–2 * [3] d. nCn–2 Databases + – cse23 708 views answer comment Share Follow Print 0 reply Please log in or register to add a comment.
Best answer 2 2 votes given that Every (n – 2) attributes of R forms Candidate key. so no. of super key = every (n – 2) combination out of n OR every (n – 1) combination out of n OR every (n ) combination out of n =ncn-2 + ncn-1 +ncn = ncn-2 +n+1 B is correct saurabh rai answered Jan 14, 2017 • selected Jan 14, 2017 by Sushant Gokhale saurabh rai comment Share Follow See all 2 Comments 2 2 Comments reply cse23 commented Jan 14, 2017 reply Follow flag can u plz elaborate.. wat i thought is if every n-2 is CK so we must include n-2 element in SK then we are left with only 2 attribute each having 2 possibility(it is present in super key or not present) so we have 2*2 =4 SK possible 0 0 replyShare Kantikumar commented Jan 14, 2017 reply Follow flag According to this approach, total SK will be ( nCn-2 * 4). This calculates duplicate SKs. Now we'll again have to remove those duplicate SKs. So better thing is not to calculate them in first place. 1 1 replyShare Please log in or register to add a comment.
