please help me to optimise this sql query, it taks long time to return result.

SELECT count( pagerno ) AS total
FROM tbldetails s1
WHERE s1.ccode = '07122009012807953'
AND s1.col1 <> 'invalid'
AND s1.col6 <= '2009-12-15'
AND s1.col6 = (
SELECT MAX( s2.col6 )
FROM tbldetails s2
WHERE s1.pagerno = s2.pagerno
AND s2.ccode = '07122009012807953')