You're correct, my forum is only open to registered users. I don't have the field user_name in my mlf2_entries table. If so, it would have been easy I'm running 2.3.4, and the missing "2" in the db prefix of my original post may have suggested I was running an older version.

And by username I mean the name with which you log in, for example, Wagner and Alfie. I don't want to show the real names people have in their profiles.

Thanks for the suggestion, I'll try to play around with joining mlf2_entries.user_id = mlf2_userdata.user_name