Problem with WHERE .. IN

[muhammad subair]

I have table post (id INT and parent VARCHAR)

+------+-------------+
| id   | parent      |
+------+-------------+
|    1 | 0           |
|    2 | 0           |
|    3 | 1           |
|    4 | 0           |
|    5 | 1           |
|    6 | 0           |
|    7 | 1,5         |
|    8 | 1,5         |
|    9 | 1,5         |
|   10 | 5,7,11      |
|   11 | 1,5,7,10    |
|   12 | 1,5,7,10,11 |
+------+-------------+

SELECT id FROM post WHERE where id IN (SELECT parent FROM post WHERE id =
10);
+------+
| id   |
+------+
|    5 |
+------+

whereas the results I want is

+------+
| id   |
+------+
|    5 |
|    7 |
|   11 |
+------+

Please tell me, where is wrong

Thanks & Regards
-- 
Muhammad Subair
[phone]