How can MySQL interpret the number and string, having no delimiter, as a date?

If a string or number, even without any delimiter, in the format of YYYYMMDDHHMMSS or YYMMDDHHMMSS is making sense as the date is provided then MySQL interpret that string as a valid date.

Examples are given for valid as well as invalid dates −

mysql> Select Timestamp(20171022040536);
+---------------------------+
| Timestamp(20171022040536) |
+---------------------------+
| 2017-10-22 04:05:36       |
+---------------------------+
1 row in set (0.00 sec)

mysql> Select Timestamp('20171022040536');
+-----------------------------+
| Timestamp('20171022040536') |
+-----------------------------+
| 2017-10-22 04:05:36         |
+-----------------------------+
1 row in set (0.00 sec)

mysql> Select Timestamp('171022040536');
+---------------------------+
| Timestamp('171022040536') |
+---------------------------+
| 2017-10-22 04:05:36       |
+---------------------------+
1 row in set (0.00 sec)

Above queries shows the examples of valid string as well number which can be interpreted as date values by MySQL.

mysql> Select Timestamp('20171022048536');
+-----------------------------+
| Timestamp('20171022048536') |
+-----------------------------+
| NULL                        |
+-----------------------------+
1 row in set, 1 warning (0.00 sec)

Above query is the example for the invalid string. MySQL returns NULL because the string is having wrong value (85) for a minute.

mysql> Select Timestamp('20171322040536');
+-----------------------------+
| Timestamp('20171322040536') |
+-----------------------------+
| NULL                        |
+-----------------------------+
1 row in set, 1 warning (0.00 sec)

In above query, MySQL returns NULL because the string is having wrong value (13) for a month.