with rests as
        (select to_date('12.01.2010', 'dd.mm.yyyy') date_rest, 100 rest from dual
         union all
         select to_date('10.02.2010', 'dd.mm.yyyy') date_rest, 800 rest from dual
         union all
         select to_date('15.04.2010', 'dd.mm.yyyy') date_rest, 0 rest from dual
         union all
         select to_date('11.09.2010', 'dd.mm.yyyy') date_rest, 400 rest from dual
         union all
         select to_date('01.06.2010', 'dd.mm.yyyy') date_rest, 0 rest from dual
         union all
         select to_date('01.07.2010', 'dd.mm.yyyy') date_rest, 0 rest from dual
         union all
         select to_date('12.07.2010', 'dd.mm.yyyy') date_rest, 300 rest from dual),
    dates as
        (select trunc(last_day(add_months(:begin_date, level - 1))) date_report
           from dual
         connect by level <= months_between(trunc(:end_date, 'mm'), trunc(:begin_date, 'mm')) + 1)
  select date_report as "Отчетная дата"
       , coalesce((date_report - min(date_rest) over (partition by rn2)) * has_rest, 0) as "Дней просрочки"
    --       , has_rest
    --       , rest
    --       , min(date_rest) over (partition by rn2)
    from (select date_report
               , date_rest
               , has_rest
               , rest
               , row_number() over (order by date_report) - row_number() over(partition by has_rest order by date_report) rn2
            from (select date_report
                       , date_rest
                       , coalesce(rest, last_value(rest ignore nulls) over (order by date_report), 0) rest
                       , case when coalesce(rest, last_value(rest ignore nulls) over (order by date_report), 0) > 0 then 1 else 0 end has_rest
                    from (  select d.date_report
                                 , max(r.date_rest) keep (dense_rank first order by d.date_report) date_rest
                                 , max(r.rest) keep (dense_rank first order by d.date_report) rest
                              from dates d left join rests r on (r.date_rest between trunc(date_report, 'mm') and date_report)
                          group by date_report)))
order by 1
/