SQL: Maximum possible date range by group, Sql Server

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create table t ([begindate] date, [enddate] date, [id] int) ; 
insert into t ([begindate], [enddate], [id]) values 
  ('2015-07-01', '2015-07-12', 1)
, ('2015-07-01', '2015-07-12', 1)
, ('2015-07-11', '2015-07-15', 1)
, ('2015-07-18', '2015-08-04', 1)
, ('2015-06-28', '2015-07-04', 2)
, ('2015-06-28', '2015-07-03', 2)
, ('2015-06-29', '2015-07-04', 2)
, ('2015-07-03', '2015-07-15', 2)
, ('2015-07-17', '2015-07-20', 2) ;

/* -- dates --*/
    declare @fromdate date, @thrudate date;
    select  @fromdate = min(begindate), @thrudate = max(enddate) from t;
    ;with n as (select n from (values(0),(1),(2),(3),(4),(5),(6),(7),(8),(9)) t(n))
    , dates as (
      select top (datediff(day, @fromdate, @thrudate)+1) 
          [Date]=convert(date,dateadd(day,row_number() over(order by (select 1))-1,@fromdate))
      from n as deka cross join n as hecto cross join n as kilo
                     cross join n as tenK cross join n as hundredK
       order by [Date]
    )
    , cte as (
    select
        t.id
      , d.date
      , grp = row_number() over (partition by t.id order by d.date)
            - datediff(day,@fromdate,d.date)
    from dates d
      inner join t
        on d.date >= t.begindate
       and d.date <= t.enddate
    group by t.id, d.date
    )
    select 
        BeginDate = convert(char(10),min(cte.date),120)
      , EndDate   = convert(char(10),max(cte.date),120)
      , id
    from cte
    where id is not null
    group by id, grp
    order by id, BeginDate

View schema
Execution time: 0,11 sec, rows selected: 5, rows affected: 9, absolute service time: 0,25 sec