MySQL Operators with Date Represented as String

Such kind of calculations can cause unpredictable result because when the date is represented as MySQL string then MySQL tries to perform numeric operations on a string by taking only the first that appears. Following examples will clarify it −

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)