order by inside group_contact mysql - mysql

Question

I have a below mysql query. It's returns wrong value. Please HELP ME to resolve this issue.
SELECT
T1.PARENT_ID,
GROUP_CONCAT(
IF(T2.PROPERTIES IS NULL, "NA", T2.PROPERTIES)
ORDER BY T1.ORDER_INDEX ASC
) AS DATA
FROM TABLE_1 T1
JOIN TABLE_2 T2
ON T1.ID=T2.ID
WHERE T1.AUTHOR="123"
GROUP BY T1.PARENT_ID
ORDER BY T1.PARENT_ID;
Mysql Version ===> 5.0.27-standard-log
The above query returns:
+-----------+---------------+
| parent_id | data |
+-----------+---------------+
| 12345 | te,test1,test |
| 23456 | NA |
+-----------+---------------+
2 rows in set (0.00 sec)
_
But, it should be:
+-----------+---------------+
| parent_id | data |
+-----------+---------------+
| 12345 | NA,test1,test |
| 23456 | NA |
+-----------+---------------+
2 rows in set (0.00 sec)
-
-
########################### TABLE DATA ############################
mysql> select * from Table_1;
+----+-----------+--------+-------------+
| id | parent_id | author | order_index |
+----+-----------+--------+-------------+
| 1 | 12345 | 123 | 3 |
| 2 | 12345 | 123 | 1 |
| 3 | 23456 | 123 | 1 |
| 4 | 12345 | 123 | 2 |
+----+-----------+--------+-------------+
4 rows in set (0.00 sec)
mysql> select * from Table_2;
+----+------------+
| id | properties |
+----+------------+
| 1 | test |
| 2 | NULL |
| 3 | NULL |
| 4 | test1 |
+----+------------+
4 rows in set (0.00 sec)
-
-
########################### TABLE MODEL ############################
mysql> desc Table_1;
+-------------+-----------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------------+-----------+------+-----+---------+-------+
| id | int(11) | NO | PRI | | |
| parent_id | char(100) | YES | | NULL | |
| author | char(100) | YES | | NULL | |
| order_index | int(11) | YES | | 0 | |
+-------------+-----------+------+-----+---------+-------+
4 rows in set (0.00 sec)
mysql> desc Table_2;
+------------+---------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+------------+---------+------+-----+---------+-------+
| id | int(11) | NO | PRI | | |
| properties | text | YES | | NULL | |
+------------+---------+------+-----+---------+-------+
2 rows in set (0.00 sec)