Table :- test
category_id   | category_name          | main_category | 
+-------------+------------------------+---------------+
|           1 | One                    |             0 | 
|           2 | Two                    |             0 | 
|           3 | Three                  |             0 | 
|           4 | Four                   |             0 | 
|           5 | Six                    |             1 | 
|           6 | Seven                  |             1 | 
|           7 | Eight                  |             1 | 
|           8 | Twelve                 |             2 | 
|           9 | Thirteen               |             2 | 
|          10 | Nine                   |             5 | 
|          11 | Five                   |             0 | 
|          12 | Ten                    |            10 | 
|          13 | Eleven                 |             5 | 

##</code><code>##

One    
  Six
    Nine
      Ten
    Eleven
  Seven
  Eight
	 
Two 
  Twelve
  Thirteen

Three
Four 
Five

##</code><code>##

 Query 1 :- Select category_id from test where main_category='0';
 Query 2 :- Select category_id from test where main_category=(result from query 1)