La solución del libro "Microsoft® SQL Server ® 2012 T-SQL de alto rendimiento con funciones de ventana"
;with C1 as(
select GroupID, FromDate as ts, +1 as type, 1 as sub
from dbo.table_name
union all
select GroupID, dateadd(day, +1, ToDate) as ts, -1 as type, 0 as sub
from dbo.table_name),
C2 as(
select C1.*
, sum(type) over(partition by GroupID order by ts, type desc
rows between unbounded preceding and current row) - sub as cnt
from C1),
C3 as(
select GroupID, ts, floor((row_number() over(partition by GroupID order by ts) - 1) / 2 + 1) as grpnum
from C2
where cnt = 0)
select GroupID, min(ts) as FromDate, dateadd(day, -1, max(ts)) as ToDate
from C3
group by GroupID, grpnum;
Crear tabla:
if object_id('table_name') is not null
drop table table_name
create table table_name(GroupID varchar(100), FromDate datetime,ToDate datetime)
insert into table_name
select 'A', '01/01/2012', '12/31/2012' union all
select 'A', '12/01/2013', '11/30/2014' union all
select 'A', '01/01/2015', '12/31/2015' union all
select 'A', '01/01/2015', '12/31/2015' union all
select 'A', '02/01/2015', '03/31/2015' union all
select 'A', '01/01/2013', '12/31/2013'
