This is one of those cases where it really depends on the skills and strengths of your development team.

If you have a clear line between db devs and front-end devs, then I would say this is something that should be done in a stored proc (since it's very database specific and probably will not translate well to other dbs if you ever decide to switch).

If you don't have that luxury or you're a one man shop, it would depend on where you're comfortable doing the work. As for efficiency, I really wouldn't worry about it (at first) - both languages (perl and transact sql) have enough power and magic to work efficiently (but then again, both give you more than enough rope to do it poorly).