Often it can help to crunch the code and database down to just enough to show the issue. At some point during the "crunching" process you will either have an epiphany, or you'll reduce things to a point where you can post sample code and data for us to look at.

Note that DBD::AnyData can often be used to provide a self contained script that includes the data, or use DBD::SQLite to populate a database on the fly. If it's a MySQL problem you can use the same technique of populating the database with test data in your sample script, but that reduces the number of monks who may be able to help diagnose the issue somewhat (they'll probably need a MySQL server available).