加法、减法、乘法和除法运算符如何处理 MySQL 表中存储的日期值？

mysql> select * from example;
+------------+
| orderdate  |
+------------+
| 二017-05-二5 |
+------------+
1 row in set (0.00 sec)

mysql> select orderdate+10 from example;
+--------------+
| orderdate+10 |
+--------------+
|     二0170535 |
+--------------+
1 row in set (0.00 sec)

mysql> select orderdate*10 from example;
+--------------+
| orderdate*10 |
+--------------+
|    两01705两50 |
+--------------+
1 row in set (0.00 sec)

mysql> select orderdate-10 from example;
+--------------+
| orderdate-10 |
+--------------+
|     两0170515 |
+--------------+
1 row in set (0.00 sec)

mysql> select orderdate/10 from example;
+--------------+
| orderdate/10 |
+--------------+
|    二01705两.5 |
+--------------+
1 row in set (0.00 sec)