diviser la plage de dates en mois

La requête suivante devrait faire l'affaire. Le CTE (le WITH clause) génère dynamiquement des données de mois que nous pouvons utiliser pour nous joindre.

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