I'm sorry if I'm misunderstanding something, but why are you using hashes to join with when the database can do the work for you.

my $sql1 = qq {
SELECT a.*, b.*, c.*
FROM table1 a,
     table2 b,
     table3 c
WHERE a.primary_key = b.foreign_key
and a.foreign_key2 = c.foreign_key2
};
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The join syntax may be slightly different depending on your database and the flavor of SQL, but hopefully that should be a lot easier than trying to join by hash.