No of Super Key

Question

R (A1, A2, ….An) and every (n-2) attributes of R forms a candidate key. How many super
keys are there in R?

a) $_{n-2}^{n}\textrm{C}$

b) $_{n-2}^{n}\textrm{C}$ * 4

c) $_{n-2}^{n}\textrm{C}$ * n

d) $_{n-2}^{n}\textrm{C}$ + n +1

Comments

@ joshi_nitish why set theory concept is not applicable here , plz tell

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@sumit,

you can use it if you want to.

total subset are $2^n$, now all those subsets which are of size >=n-2 will be super keys

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@ joshi_nitish  iam  asking like : suppose a relation  R1(A,B,C)  , CK = { A,B,C} 

superkeys are  =  4+4+4 - ( 2+2+2) +1  

if here i try to apply then there will be n terms i stuck in it ?

how you would apply plz explain

Answer 1

nCn-2+n+1 super keys.

Comments

Option d) works properly for n=4 then number of sk will be 11

But for n=3 no of superkeys should be 4 and according to option d) it shows 7 superkeys

Someone please correct me if I m wrong??