Question

I’ve this db structure:

Message  

msg_by     usertype     message    
2             U         how are you ? 
1             A         i'm fine


SimpleUser 

id          fullname    
1           mike    
2           john


AdminUser    

id           fullname
1            frank     
2            lucas

Ok, i know it’s not correct to split users into two table but i’ve inherited this project.

My question is how to make a query making joining Message with SimpleUser and AdminUser … with the result to have the correct name for each message based to usertype: if U the message is from SimpleUser table, if A the message is from AdminUser

Thank you for your help!

Answer 1

With a UNION:

SELECT fullname, message FROM msg_by JOIN SimpleUser ON(msg_by = SimpleUser.id)
  WHERE usertype = "U"

UNION ALL

SELECT fullname, message FROM msg_by JOIN AdminUser ON(msg_by = AdminUser.id)
  WHERE usertype = "A"