How to get the difference between two dates rounded to hours
I think a more complete answer is
select time_format(timediff(onedateinstring,anotherdateinstring),'%H:%i:%s')
This allows you to see the hours, minutes, seconds, etc. that you wish to see in the format you want...
More information on time_format: http://dev.mysql.com/doc/refman/5.7/en/date-and-time-functions.html#function_time-format
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 |
+-----------------------------------------------------------------------------+
Use TIMESTAMPDIFF for exact number of hours :
SELECT
b.`Start_Date`,
b.`End_Date`,
TIMESTAMPDIFF(HOUR, b.`Start_Date`, b.`End_Date`) AS `HOURS`
FROM my_table b;