select time_to_sec(timediff('2010-09-01 03:00:00', '2010-09-01 00:10:00' )) / 3600;
+-----------------------------------------------------------------------------+
| time_to_sec(timediff('2010-09-01 03:00:00', '2010-09-01 00:10:00' )) / 3600 |
+-----------------------------------------------------------------------------+
| 2.8333 |
+-----------------------------------------------------------------------------+