Linking old comments to current accounts?

Howdy all. I’m a relatively new convert to WP having moved my blogs from ExpressionEngine to WP a couple of months ago. One thing I’d like to do, but haven’t been clever enough to figure out, is come up with an SQL query that would go through the database and associate old comments with current user accounts.

I figured the simplest way would be to do it by email address, but I’m not at all familiar with WP’s database schema or, for that matter, SQL. Has anyone come up with something similar that they could share?