Vous pouvez utiliser un CTE récursif pour construire votre liste de 30 jours, puis la joindre à vos données
--test
select cast('05 jan 2011' as datetime) as DT, 1 as val into #t
union all select CAST('05 jan 2011' as datetime), 1
union all select CAST('29 jan 2011' as datetime), 1
declare @start datetime = '01 jan 2011'
declare @end datetime = dateadd(day, 29, @start)
;with amonth(day) as
(
select @start as day
union all
select day + 1
from amonth
where day < @end
)
select amonth.day, count(val)
from amonth
left join #t on #t.DT = amonth.day
group by amonth.day
>>
2011-01-04 00:00:00.000 0
2011-01-05 00:00:00.000 2
2011-01-06 00:00:00.000 0
2011-01-07 00:00:00.000 0
2011-01-08 00:00:00.000 0
2011-01-09 00:00:00.000 0
...
