in reply to mysql's join too slow; using Perl to compare two tables
Are you using indices, and if so, are you certain that the database is doing index scans instead of sequential scans in your query? Before you give up on MySQL and try to solve the problem with Perl, you should have a look at the EXPLAIN and ANALYZE statements.
Since you didn't mention which version of MySQL you're using, I'll take a guess and include Optimizing Queries with EXPLAIN for versions 3.23 through 4.1.
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