to get duration between time in MySQL- query

SELECT DATE(creation_date) `dt`, creation_date, last_modified, SEC_TO_TIME( UNIX_TIMESTAMP(last_modified) - UNIX_TIMESTAMP(creation_date) ) `duration`, `action`
FROM sms_out_message_analyze
GROUP BY `dt`, `duration`
HAVING `dt` = '2011-01-12'
LIMIT 1500;