SQl Query-No of days in a month

declare @year int, @month int select @year = 2012, @month = 2 select datediff(day, dateadd(day, 0, dateadd(month, ((year(effectiveDate) - 1900) * 12) + month(effectiveDate) - 1, 0)), dateadd(day, 0, dateadd(month, ((year(effectiveDate) - 1900) * 12) + month(effectiveDate), 0)) )