SQL udvidet "NOT IN" query

PHP kode 

 $bankresult = mysql_query("SELECT * FROM bankposteringer WHERE maaned = $maned");
 
 
 while ($bankrow = mysql_fetch_array($bankresult))
 
 {
 
     $bankbelob = $bankrow['belob'];
     
 $economicresult = mysql_query("SELECT * FROM economic WHERE belob = '$bankbelob' AND used = 0 AND maaned = $maned GROUP BY belob");
 $ecorow = mysql_fetch_array($economicresult);
 
 $ecobelob = $ecorow['belob'];
 $ecoindex = $ecorow['index'];
 
 
     //echo "$ecobelob index.: $ecoindex\n";
     
     mysql_query("UPDATE economic SET used = '1' WHERE index = $ecoindex AND maaned = $maned");
 
 }

SQL kode 

 SELECT t1.key, COUNT(t1.key)-(SELECT COUNT(t2.key) FROM otherTable t2 WHERE t2.key = t1.key) AS n FROM table t1
 WHERE COUNT(t1.key) - (SELECT COUNT(t2.key) FROM otherTable t2 WHERE t2.key = t1.key) > 0

Kode 

key   | n
10001 | 1

SQL kode 

 SELECT * FROM bankposteringer WHERE maaned = $maned
 SELECT * FROM economic WHERE belob = '$bankbelob' AND used = 0 AND maaned = $maned GROUP BY belob

Tak for minus.
Men jeg holder stadig på, at det er et design issue, som sandsynligvis kan løses mere elegant ved at ændre i strukturen istedet for brute force.