SELECT COUNT(*) FROM tA
WHERE
TO_DAYS(regis_date) > TO_DAYS('2003-1-1') AND
TO_DAYS(regis_date) < TO_DAYS('2003-3-31')
WHERE
TO_DAYS(regis_date) > TO_DAYS('2003-1-1') AND
TO_DAYS(regis_date) < TO_DAYS('2003-3-31')
.... WHERE regis_date > '2003-01-01' AND regis_date < '2003-03-31'就行了