SQL Server: Gap / Island, 365 day "contiguous" block - sql-server

Question

I have a table that looks like this:-
tblMeterReadings
id meter date total
1 1 03/01/2014 100.1
1 1 04/01/2014 184.1
1 1 05/01/2014 134.1
1 1 06/01/2014 132.1
1 1 07/01/2014 126.1
1 1 08/01/2014 190.1
This is an 8 day "contiguous block" from '2014-01-03' to '2014-01-08'.
In the real table there are "contiguous blocks" of years in length.
I need to select the MOST RESCENT CONTINUOUS 365 DAY BLOCK (filtered by meter column). If 365 cannot be found, then it should select next largest continuous block.
When I say CONTINUOUS I mean there must be no days missing.
This is beyond me, so if someone can solve... I will be very impressed.

Answer 1

using distinct to not count days with 2 sets of data
declare #gapdays int = 2 -- replace this with 365 in your case
;with x as
(
select datediff(d, '2014-01-01', [date])-dense_rank()over(order by [date]) grp
,[date]
from #t
)
select top 1 max([date]) last_date, min([date]) first_date, count(distinct [date]) days_in_a_row
from x
group by grp
having count(distinct [date]) >= #gapdays
order by max([date]) desc

Answer 2

There you go:
declare #tblMeterReadings table (id int, meter int, [date] date, total money)
insert into #tblMeterReadings ( id, meter, date, total )
values
(1, 1, '03/01/2014', 100.1),
(1, 1, '04/01/2014', 184.1),
(1, 1, '05/01/2014', 134.1),
(1, 1, '06/01/2014', 132.1),
(1, 1, '07/01/2014', 126.1),
(1, 1, '08/01/2014', 190.1),
(1, 1, '10/01/2014', 200.1),
(1, 1, '12/01/2014', 202.1),
(1, 1, '13/01/2014', 204.1)
;with data as (
select i = datediff(day, '2014', [date]), *
from #tblMeterReadings l
)
, islands as (
select island = l.i - row_number() over (order by i), l.*
from data l
)
, spans as (
select l = min(i), r = max(i)
from islands i
group by island
)
select *
from spans s
left join data l on s.l = l.i
left join data r on s.r = r.i
Most recent continuous block not exceeding 365 days in length will be as follows:
select top 1 *
from spans s
left join data l on s.l = l.i
left join data r on s.r = r.i
where s.l - s.r < 365
order by s.l - s.r desc, s.r desc

Answer 3

With recursive CTE and datepart(dayofyear, date):
with cte as
(
select id, meter, date, datepart(dayofyear, date) as x, cast(1 as int) as level, t1.date as startDate from tblMeterReadings t1
where meter = 1
and not exists(select * from tblMeterReadings t2 where (datepart(dayofyear, t1.date) - 1) = datepart(dayofyear, t2.date))
union all
select t1.id, t1.meter, t1.date, datepart(dayofyear, t1.date) as x, t2.level + 1, t2.startDate from tblMeterReadings t1
inner join cte t2 ON (datepart(dayofyear, t1.date)) = (datepart(dayofyear, t2.date) + 1)
)
select TOP 365 * from cte
where cte.startDate = (select top 1 startdate
from cte
--where Level <= 365
order by Level desc, startDate desc)
order by Level desc
OPTION ( MAXRECURSION 365 )
SQL Fiddle example