I would bet it's not memory that's the issue. It's row counts.
Consider the case where you said you have one user in 32 groups. That user alone would generate POWER(2,32)-1 rows (working from memory here so check the article to be sure). That's a lot of rows.
You can try the loop I suggested but it will still have to deal with ridiculous numbers of rows.
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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