The LIMIT 1 suggestions are of course good, but a combination with sorting is perhaps not so very good. Depending on the indexes you have defined on your tables and fields, running a query which need to be sorted will --in a worst case scenario-- still first get the whole resultset, sort it and then drop all of them except the first record (due to the LIMIT 1 clause).

In similar problems I most always found that rewriting the SQL to natively return only one record (without needing to do a sorting operation followed by a LIMIT 1) gave me generally better performance.