Jak uzyskać dane z ostatniego miesiąca i dane od początku miesiąca?

Today including time info  : getdate()
Today without time info    : DATEADD(DAY, DATEDIFF(day, 0, getdate()), 0)
Tomorrow without time info : DATEADD(DAY, DATEDIFF(day, 0, getdate()), 1)
Beginning of current month : DATEADD(month, datediff(month, 0, getdate()), 0)
Beginning of last month    : DATEADD(month, datediff(month, 0, getdate())-1, 0)

więc najprawdopodobniej

WHERE dateColumn >= DATEADD(month, datediff(month, 0, getdate())-1, 0)
  AND dateColumn <  DATEADD(DAY, DATEDIFF(day, 0, getdate()), 1)