Question

I have MYSQL tables as follows

user TABLE {id INT}

profile TABLE {user_id INT, facebook_id varchar(50)}

messages TABLE {id INT, message TEXT, from_id INT, type enum('main','facebook'}

messages_to TABLE {user_id varchar(50), message_id INT}

profile.user_id REFERS To user.id
- the messages_to.message_id refers to the messages.ID column.
- the messages_to.user_id refers to profile.user_id IF messages.type = 'main' BUT
  if message_type = 'facebook' THEN messages_to.user_id REFERS to profile.facebook_id

I want to do a join query that basically selects all the messages to a specific person, but the thing is the messages_to.user_id can refer to either the person's facebook ID or the person's ID (a reference to user.id column).

So basically the query should work as follows

• it should select all the messages in messages table, and if messages.type = 'facebook' checks if messages_to.user_id equals the person’s FACEBOOK ID. (note that messages_to table stores the recipients for each messages ID)
• BUT if the messages.type = 'main' checks if the messages_to.user_id equals the person's USER ID (USER.id)

Is it possible to do a mysql join query for that efficiently?

messages_tos table stores ALL the recipients for each message in the MESSAGES table. THERE CAN be MORE THAN ONE RECIPIENT for a message.

Answer 1

I guess this is the query.

SELECT messages.*,profile.* 
FROM messages 
JOIN messages_to ON messages.id = messages_to.message_id
JOIN profile ON 
  (profile.user_id = messages_to.user_id AND messages.type = 'main') 
  OR (profile.facebook_id = messages_to.user_id AND messages.type = 'facebook')