How to join two columns to the same table [duplicate]

Answer 1

You need to join twice to the table with the user data - once for each user involved:

select uf.username from_username, ut.username to_username, message
from messages m
join aspnet_Users uf on uf.id = userfrom
join aspnet_Users ut on ut.id = userto

This sql will work in both databases you have tagged the question with (or any other).