Okay ... then perhaps MySQL can help you in a different way. I don't know if this is suitable or not, but you might create a temporary table of the columns you're comparing, and put an index on it, and insert the key fields of both tables. Then you can select from all three columns using eq (which I (perhaps falsely) presume should work well in Perl).

So the temp table would hold the ordering, and you simply select which of the other two tables holds the match for the record...the first, the second, or both.

It may not be a good solution for you, if speed and/or database space is limited, but it's the only thing I can think of. (I know diddly-squat about fancy collation sequences....)

...roboticus