How many secondary index can be made with n attributes, I am getting as (2^n)-1 is it correct?
My approach is: we can check with one by one merging with attributes as we do in case of superkey.
I found this explanation online:
For n = 5 , we have :
No of secondary indices possible = 5P1 + 5P2 ...........+ 5P5
= (5! / 4!) + (5! / 3!) + (5! / 2!) + (5! / 1!) + (5! / 0!)
= 5 + 20 + 60 + 120 + 120
= 325
Hence no of secondary indices possible with 5 attributes = 325
Is the above explanation is correct?