docs/en/sql-reference/sql-functions/date-time-functions/timediff.md
Returns the difference between two DATETIME expressions.
The return value must be of the TIME type.
TIME TIMEDIFF(DATETIME expr1, DATETIME expr2)`
MySQL > SELECT TIMEDIFF(now(),utc_timestamp());
+----------------------------------+
| timediff(now(), utc_timestamp()) |
+----------------------------------+
| 08:00:00 |
+----------------------------------+
MySQL > SELECT TIMEDIFF('2019-07-11 16:59:30','2019-07-11 16:59:21');
+--------------------------------------------------------+
| timediff('2019-07-11 16:59:30', '2019-07-11 16:59:21') |
+--------------------------------------------------------+
| 00:00:09 |
+--------------------------------------------------------+
MySQL > SELECT TIMEDIFF('2019-01-01 00:00:00', NULL);
+---------------------------------------+
| timediff('2019-01-01 00:00:00', NULL) |
+---------------------------------------+
| NULL |
+---------------------------------------+
TIMEDIFF