How do you join two fields in one table into a second table?

Question

I have a table which contains three fields two of which link into the same table to lookup the value (the third links to a second table)

Deployment Table
---------------------------------
INDEX,  APP,  DEVSERVER, PRODSERVER (was previously just SERVER)

Server Table
---------------------------------
INDEX, NAME

App Table
---------------------------------
INDEX, NAME

Previously, when I had just SERVER in the deployment table I was doing:

SELECT d.index, a.name as `app`, s.name as `server`
FROM deployment as `d`, app as `a`, server as `s`
WHERE d.app = a.index AND d.server = s.index

and it was working fine. But now that I want to "double dip" into the server table with DEVSERVER and PRODSERVER I've not the foggiest way how to go about it.

Answer 1

First, you should use proper join syntax. Second, you need to introduce a second join to the server table:

SELECT d.index, a.name as app, dserv.name as devserver, pserv.name as prodserver
FROM deployment d join
     app a
     on d.app = a.index join
     server dserv
     on d.devserver = dserv.index join
     server pserv
     on d.prodserver = pserv.index;