If you (almost) always query by COLA or ( COLA, COLB ), then cluster the table on ( COLA, COLB ).  Then you'll always get a seek with either of those searchesm,...

Log space will be needed, as always for any mods, but I don't think both tables exist simultaneously unless you're doing an ONLINE rebuild, which you wouldn't do if you...

Mode is quite OK to do as long as you make the initial proc just a driver proc: it adjusts param(s) as needed and then calls another, customized proc to...

I don't think you need extra space.  SQL compresses page by page (I'm assuming page compression, as row compression wouldn't save you all that much space).  Row compression only would...

You're welcome.  I started the confusion when I stated that assignment of uniquifiers was "completely arbitrary" without clarifying it.  I made it sound like the values were random over time. ...

For final prod code, I'd probably make a couple of other minor adjustments to make the code more inherently clear.  I'm a firm believer in self-documenting code, including clear variable...

SQL calls it a "uniquifier", not a "row id".  The assignment is completely arbitrary -- and totally meaningless to you.  If you're worried about getting "Abigail" Smith returned before "John"...

There's no need for any tally table nor recursion.  A simple mathematical calc is enough.  I'm almost sure this is it, although I'm extremely busy and haven't fully tested it...