Databases aren't magic. For the database to be fast at both operations, it needs to have indexes on both fields. At which point you have something similar to hashes pointing both ways.

The only real saving with a relational database is that its internal data format is likely more compact than Perl's, so the data will take less memory.

In reply to Re^2: two hashes occupying the same space by tilly
in thread two hashes occupying the same space by jfroebe

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