La seguente query dovrebbe fare il trucco. Il CTE (il WITH clausola) genera dinamicamente alcuni dati del mese che possiamo utilizzare per unirci.
declare @test table (
userid char(1),
project char(4),
startdate datetime,
enddate datetime)
insert into @test
select 'A', 'abc1', '1/1/2011', '12/31/2011'
union select 'A', 'abc2', '1/1/2011', '5/1/2011'
union select 'B', 'xyz1', '1/1/2011', '3/1/2011'
--select * from @test
;with MonthList as (
select
DATEADD(month, M, '12/1/1899') as 'FirstDay',
dateadd(day, -1, dateadd(month, M + 1, '12/1/1899')) as 'LastDay',
DATEADD(month, M + 1, '12/1/1899') as 'FirstDayNextMonth'
from (
select top 3000 ROW_NUMBER() over (order by s.name) as 'M'
from master..spt_values s) s
)
select
t.userid, t.project, ml.FirstDay, ml.LastDay
from
@test t
inner join MonthList ml
on t.startdate < ml.FirstDayNextMonth
and t.enddate >= ml.FirstDay
