SELECT a.id
FROM
    (SELECT O1.lft, O1.id, COUNT(O2.id)
   FROM content_tree AS O1, content_tree AS O2
   WHERE O1.lft BETWEEN O2.lft AND O2.rgt
   GROUP BY O2.id
   ORDER BY O1.lft;
) AS a


MySQL said: 
#1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '' at line 8