Does a dual key or single key lookup perform better on a table with a lot of data?

We have table where rows unique between 3 columns. GroupA, GroupB, ProductID.

GroupA & GroupB are used in combinations to Group sets of ProductIDs and will always be used to lookup sets of productIDs. Sometimes a ProductID will be used in in the query also.

I wasnt sure if there would be any performance gains from combining GroupA and GroupB into the same column so that the index is clustered.

GroupA | GroupB | ProductID
   ----------------------------
   A1     | B1     | 1
   A1     | B1     | 99
   A1     | B2     | 1
   A1     | B2     | 99
   A2     | B1     | 1
   A2     | B1     | 99
   A2     | B2     | 1
   A2     | B2     | 99

Dual group method above OR Single group method below.

GroupAB | ProductID
   --------------------
   A1-B1   | 1
   A1-B1   | 99
   A1-B2   | 1
   A1-B2   | 99
   A2-B1   | 1
   A2-B1   | 99
   A2-B2   | 1
   A2-B2   | 99

   GroupA | GroupB | GroupAB
   ----------------------------
   A1     | B1     | A1-B1
   A1     | B2     | A1-B2
   A2     | B1     | A2-B1
   A2     | B2     | A2-B2

I don't think it would really matter. You can cluster on both without concatenating them:

CREATE CLUSTERED INDEX ixc_MyIndexName ON MyTable (GroupA, GroupB)

Which will accomplish the same thing but not require you to modify your data.

StackExchange Database Administrators Q#18364, answer score: 2