Решение:
DECLARE @StartDate DATETIME
,@EndDate DATETIME;
SELECT @StartDate = '20110105'
,@EndDate = '20110815';
SELECT DATEADD(MONTH, DATEDIFF(MONTH, 0, DATEADD(MONTH, v.number, @StartDate)), 0) AS FirstDay
--or Andriy M suggestion:
--SELECT DATEADD(MONTH, DATEDIFF(MONTH, 0, @StartDate) + v.number, 0) AS FirstDay
INTO #Results
FROM master.dbo.spt_values v
WHERE v.type = 'P'
AND DATEDIFF(MONTH, @StartDate, @EndDate) >= v.number;
SELECT *
FROM #Results;
DROP TABLE #Results;
Результаты:
FirstDay
-----------------------
2011-01-01 00:00:00.000
2011-02-01 00:00:00.000
2011-03-01 00:00:00.000
2011-04-01 00:00:00.000
2011-05-01 00:00:00.000
2011-06-01 00:00:00.000
2011-07-01 00:00:00.000
2011-08-01 00:00:00.000