Unless I'm misinterpreting these odd requirements, this is really simple.
It depends on the number of selections you make from the set. So with 12 columns, and if you want to uniquely select 5 of those columns, the formula is:
12! / 5!*7! or in SQL:
SELECT 2*3*4*5*6*7*8*9*10*11*12/((2*3*4*5)*(2*3*4*5*6*7));
This assumes you really want combinations and not permutations. In the latter, order is important.
Reference: http://en.wikipedia.org/wiki/Combination
My thought question: Have you ever been told that your query runs too fast?
My advice:
INDEXing a poor-performing query is like putting sugar on cat food. Yeah, it probably tastes better but are you sure you want to eat it?
The path of least resistance can be a slippery slope. Take care that fixing your fixes of fixes doesn't snowball and end up costing you more than fixing the root cause would have in the first place.
Need to UNPIVOT? Why not CROSS APPLY VALUES instead?[/url]
Since random numbers are too important to be left to chance, let's generate some![/url]
Learn to understand recursive CTEs by example.[/url]
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