how to subtract time in my sql

check this query

select time_to_sec(timediff('2010-09-01 03:00:00',
                             '2010-09-01 00:10:00' ))

you can pass the parameters also to that query

or you can get details from this link

http://dev.mysql.com/doc/refman/5.1/en/date-and-time-functions.html#function_timestampdiff

try it..