Doubled Left join query comes out NULL

[Alchemy]

When I run this query on my server, the results are completely empty... I'm trying to learn how to write complicated sql queries so that I don't have to have hundred of simple ones running on every page of my CMS.... Here;s the query in question.

[code]SELECT
quotes.*,
user.userid, user.username, user.displaygroupid, user.usergroupid,
usergroup.usergroupid, usergroup.opentag, usergroup.closetag,
IF(displaygroupid=0, user.usergroupid, displaygroupid) AS displaygroupid
FROM cms_quotes AS quotes
LEFT JOIN vb_user AS user ON(quotes.quote_added_by = user.userid)
LEFT JOIN vb_usergroup AS usergroup ON(user.displaygroupid = usergroup.usergroupid)
WHERE quotes.quote_approved IS NOT NULL
ORDER BY RAND() LIMIT 1[/code]

Now, since there are table entires that have quote_approved not being null... I don't understand why the query runs without error, but then the results come in null.... any help would be greatly appreciated.

[printf]

Is [b]quote_approved[/b] defined as being NULL, if it has no value?

printf

[fenway]

Just to confirm, the join will never "null out" anything in the quotes table....