DECLARE @PreviousMonthStart DATETIME

DECLARE @PreviousMonthEnd DATETIME

SET @PreviousMonthStart = DATEADD(m,DATEDIFF(m,0,GETDATE())-1,0)

SET @PreviousMonthEnd = DATEADD(ms,-2,DATEADD(month, DATEDIFF(month, 0, GETDATE()), 0))

PRINT @PreviousMonthStart

PRINT @PreviousMonthEnd

SELECT * FROM MyTable

WHERE MyDate >= @PreviousMonthStart

AND MyDate < @PreviousMonthEnd