加法、减法、乘法和除法运算符如何处理表示为 MySQL 字符串的日期？

mysql> select '2017-10-17' + 20;
+-------------------+
| '2017-10-17' + 20 |
+-------------------+
|      2037         |
+-------------------+
1 row in set, 1 warning (0.00 sec)

mysql> select '2017-10-25' - 17;
+-------------------+
| '2017-10-25' - 17 |
+-------------------+
|              2000 |
+-------------------+
1 row in set, 1 warning (0.00 sec)

mysql> select '2017-10-17' * 2;
+-------------------+
| '2017-10-17' * 20 |
+-------------------+
|              4034 |
+-------------------+
1 row in set, 1 warning (0.00 sec)

mysql> select '2017-05-25'/5;
+----------------+
| '2017-05-25'/5 |
+----------------+
|          403.4 |
+----------------+
1 row in set, 1 warning (0.00 sec)