Question

This sounds simple, and probably is…

Alright, so I have two tables, users and messages.
Formatted like so:

users
ID | username
1  | im_a_user
2  | another_user

messages
ID | FROM | TO | CONTENT
1  | 1    | 2  | Blah blah blah...
2  | 2    | 1  | Hello, World!
3  | 2    | 1  | Another message.

If you didn’t guess, columns FROM and TO are references to the ID from the table users.

Anyhow, I’d like to make a query that returns something like this:

ID | FROM         | TO           | CONTENT
1  | im_a_user    | another_user | Blah blah blah...
2  | another_user | im_a_user    | Hello, World!
3  | another_user | im_a_user    | Another message.

I’ve done this before with JOINS, but I’m a bit rusty, and I was wondering if there was a simpler way.. If not, a query using a JOIN is fine.

Answer 1

JOINs exist exactly for things like that. You need a query like this:

SELECT
    m.id,
    sender.username AS sender,
    recipent.username AS recipient,
    m.content
FROM messages m
    INNER JOIN users sender
    ON sender.id = `m.from`
    INNER JOIN users recipent
    ON recipient.id = m.to

If you have NULLs on columns TO or FROM, change the apropriate INNER JOIN to a LEFT OUTER JOIN.

As a side note, I’d recommend you refrain from using SQL reserved words such as FROM as column names.