Question

I have two tables as below:

Users

• ID
• UserName
• Email

Messages

• ID
• Message
• FROMUSER
• TOUSER

FROMUSER and TOUSER have a Foreign key reference to ID in Users table.

Now I want to retrieve messages doing a join on users with the user’s email addresses, as below

| ID | Message | FROMEMAIL | TOEMAIL |

I could write a query as below.

SELECT Step1.*, 
       users.email as ToUser 
  FROM (SELECT messages.*, 
               users.email as fromuser 
          FROM messages 
          JOIN users on messages.fromuser = users.ID) as Step1 
  JOIN users on step1.touser = users.ID

Is there any simple way I can achieve this without the subquery?

Answer 1

Just join the Users table twice:

SELECT Message, uf.Email AS FromEmail, ut.Email AS ToEmail
FROM Messages
JOIN Users uf ON Messages.FromUser = uf.Id
JOIN Users ut ON Messages.ToUser = ut.Id