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sql date parameter in query
declare @StartDate DATE
declare @EndDate   DATE
SET @StartDate = DATEADD(MONTH, -12, '2012-08-01')
SET @EndDate = DATEADD(MONTH, +1, '2012-08-01')

DECLARE
  @InputDate DATE,
  @StartDate DATE,
  @EndDate   DATE

SET
  @InputDate = '2012-08-01'

SET
  @StartDate = DATEADD(MONTH, DATEDIFF(MONTH, 0, @InputDate) - 11, 0)

SET
  @EndDate   = DATEADD(DAY, -1, DATEADD(MONTH, 12, @StartDate))

WHERE
      table.dateField >= '2011-09-01'
  AND table.dateField <  '2012-09-01'

SET @EndDate = DATEADD(DAY, -1, @EndDate)

SET @EndDate = DATEADD(DAY, -1,DATEADD(MONTH, +1, '2012-08-01'))

declare @Date DATE='2012-08-05'
select convert(date,DateAdd(Month, DateDiff(Month, 0, @Date)-11,0)) StartDate ,
                       convert(date,DateAdd(day,-1,DateAdd(Month,1,
                       DateAdd(Month, DateDiff(Month, 0, @Date),0)))) EndDate

StartDate       EndDate
2011-09-01  2012-08-31