TIME_TO_SEC

SELECT TIME_TO_SEC('22:23:00');
+-------------------------+
| TIME_TO_SEC('22:23:00') |
+-------------------------+
|                   80580 |
+-------------------------+

SELECT TIME_TO_SEC('00:39:38');
+-------------------------+
| TIME_TO_SEC('00:39:38') |
+-------------------------+
|                    2378 |
+-------------------------+

SELECT TIME_TO_SEC('09:12:55.2355');
+------------------------------+
| TIME_TO_SEC('09:12:55.2355') |
+------------------------------+
|                   33175.2355 |
+------------------------------+
1 row in set (0.000 sec)