선분이력관리

전화table : phone_num, startdate, enddate, ratetype
요금table : ratetype, startdate, enddate, rate

select a.phone_num 전화번호,
         greatest(a.startdate,b.startdate) startdate,
         least(a.enddate,b.enddate) enddate,
         a.ratetype,
         b.rate
from 전화 a, 요금 b
where a.ratetype = b.ratetype
and b.startdate < a.enddate
and b.enddate > a.startdate
and a.phone_num = '1111111'