Extract the second. This function returns the second portion of a time or datetime value as a number from 0 to 59.
SELECT SECOND('10:05:03');
+--------------------+
| SECOND('10:05:03') |
+--------------------+
| 3 |
+--------------------+
SELECT SECOND('10:05:01.999999');
+---------------------------+
| SECOND('10:05:01.999999') |
+---------------------------+
| 1 |
+---------------------------+