SELECT MIN(if_dt) sdt
     , MAX(if_dt) edt
     , MAX(qty) qty
  FROM (SELECT if_dt, qty
             , SUM(flag) OVER(ORDER BY if_dt) grp
          FROM (SELECT if_dt, qty
                     , CASE WHEN LAG(qty) OVER(ORDER BY if_dt) < qty
                            THEN 0 ELSE 1 END flag
                  FROM t
                )
        )
 GROUP BY grp
 HAVING MAX(qty) > 0
 ORDER BY grp
;

빠른 도움 감사드립니다. ^^