Kesalahan Query MySQL Bila Tipe Varchar

SELECT * FROM `purchase_order` WHERE status = 0
# output
+----+------------+------------+---------+---------+-------------------+------------+------------+--------+---------------------+---------------------+
| id | po_number  | po_date    | site_id | status  | file_pdf          | updated_by | created_by | active | created_at          | updated_at          |
+----+------------+------------+---------+---------+-------------------+------------+------------+--------+---------------------+---------------------+
|  1 | 8100009248 | 2016-05-31 |       1 | Dikirim | 81-9248.pdf       |          2 |          2 |      1 | 2016-08-10 11:07:22 | 2016-08-15 14:15:10 |
|  2 | 8100009547 | 2016-06-21 |       2 | Dikirim | 81-9547.pdf       |          2 |          2 |      1 | 2016-08-10 11:10:51 | 2016-08-15 14:14:46 |
|  3 | 8100008792 | 2016-04-27 |       2 | Dikirim | po 8100008792.pdf |          2 |          2 |      1 | 2016-08-10 11:13:25 | 2016-08-15 14:14:11 |
|  4 | 8100008436 | 2016-03-29 |       2 | Dikirim | PO 8100008436.pdf |          2 |          2 |      1 | 2016-08-10 11:15:12 | 2016-08-15 14:20:40 |

SELECT * FROM `purchase_order` WHERE status = '0'
# output
+-----+-------------+------------+---------+--------+----------+------------+------------+--------+---------------------+---------------------+
| id  | po_number   | po_date    | site_id | status | file_pdf | updated_by | created_by | active | created_at          | updated_at          |
+-----+-------------+------------+---------+--------+----------+------------+------------+--------+---------------------+---------------------+
| 173 | F60794      | 2016-09-01 |      28 | 0      | NULL     |          4 |          4 |      1 | 2016-09-02 09:25:05 | 2016-09-02 09:25:05 |
| 190 | HAI12880807 | 2016-10-06 |      28 | 0      | pdf.pdf  |          1 |          1 |      1 | 2016-10-06 12:37:00 | 2016-10-07 22:50:38 |
+-----+-------------+------------+---------+--------+----------+------------+------------+--------+---------------------+---------------------+