Boggled by GROUP_CONCAT in query...

[Antivirus]

Working on a query and having a difficult time with this. If anyone can help i'll be very happy

My data:
For Table things...
=================
| thingid | stringcodeids |
=================
| 1 | 1 |
| 2 | 1,3,4 |
| 3 | |
| 4 | 2 |
=================

For Table stuff...
=================
| stuffid | code |
=================
| 1 | AAA |
| 2 | BBB |
| 3 | CCC |
| 4 | DDD |
| 5 | EEE |
| 6 | FFF |
=================


My query:

PHP Code:

$sql = $db->query_read("
     SELECT things*, GROUP_CONCAT(stuff.code ORDER BY code SEPARATOR ', ') AS thingcodes
     FROM things
     LEFT JOIN stuff ON stuff.stuffid IN ( things.stringcodeids )
     WHERE things.stringcodeids = 2
     GROUP BY things.thingid
"); 


Problem is that I can't get a concatenated list of related fields stuff.code based upon the string of code ids within things.stringcodeids

What I want specifically is for alias thingcodes to return 'AAA, CCC, DDD', however thingcodes is returning as empty

Thanks!