GROUP BY - do not group NULL

Question

I\'m trying to figure out a way to return results by using the group by function.

GROUP BY is working as expected, but my question is: Is it possible to have group b

Answer 1

SELECT table1.*, 
    GROUP_CONCAT(id SEPARATOR ',') AS children_ids
FROM table1
WHERE (enabled = 1) 
GROUP BY ancestor
       , CASE WHEN ancestor IS NULL
                  THEN table1.id
                  ELSE 0
         END