What are you optimizing than? Execution speedup cq load time? Are you sure that it takes significantly more time to do an additional query to the server? I guess the connection is not closed between the statement. Maybe the DB is on the same box as the webserver.

And even if it takes some additional timeframe (probably very small, test it!) for the query, is it worth the worse maintainability of perl code vs the SQL code?

I generally would answer 'no', but your situation may be different. As ppl say: only optimize the code that needs optimization. Optimization leads to less quality code, so be sure you need it. Just consider what you are doing.