我们如何忽略 MySQL DATEDIFF() 函数返回的负值？

Mysql> select * from differ;
+------------+-------------+
| OrderDate  | WorkingDate |
+------------+-------------+
| 2017-10-22 | 2017-10-29  |
| 2017-10-25 | 2017-10-30  |
| 2017-10-25 | 2017-11-30  |
+------------+-------------+
3 rows in set (0.00 sec)

mysql> Select DATEDIFF(OrderDate, WorkingDate)AS 'DIFFERENCE IN DAYS' from differ;
+--------------------+
| DIFFERENCE IN DAYS |
+--------------------+
|                 -7 |
|                 -5 |
|                -36 |
+--------------------+
3 rows in set (0.00 sec)

mysql> Select ABS(DATEDIFF(OrderDate, WorkingDate))AS 'DIFFERENCE IN DAYS' from differ;
+--------------------+
| DIFFERENCE IN DAYS |
+--------------------+
|                  7 |
|                  5 |
|                 36 |
+--------------------+
3 rows in set (0.00 sec)