How do I use the empty variable in MySQL more than once?

Question

I am trying to check for 2 empty variables in a MySQL statement but I can seem to get the syntax quite right for it. Here is what I have now and it keeps giving me an error. Can anyone please tell me how I can do this properly?

  SELECT threads, userid, username, usergroupid
    FROM " . TABLE_PREFIX . "user
   WHERE  
    " . iif(!empty($exuserids), "AND userid NOT IN ($exuserids)") . "
    " . iif(!empty($exgroups), "AND usergroupid NOT IN ($exgroups)") . "
ORDER BY threads DESC 
   LIMIT 1

Answer 1

Use:

  SELECT threads, userid, username, usergroupid
    FROM " . TABLE_PREFIX . "user
   WHERE 1 = 1 
    " . iif(!empty($exuserids), "AND userid NOT IN ($exuserids)") . "
    " . iif(!empty($exgroups), "AND usergroupid NOT IN ($exgroups)") . "
ORDER BY threads DESC 
   LIMIT 1

There needs to be a WHERE clause before you specify "AND ..." - the 1 = 1 will be optimized out. It's a trick used for dynamic SQL to make WHERE clause concatenation easier.