-- first
select *
from myTable
where year(datecolumn) = year(getdate()) and month(datecolumn) = month(getdate())
-- second
select *
from myTable
where datediff(mm, datecolumn, getdate()) = 0
-- third
declare @lodate datetime; set @lodate = dateadd(mm, datediff(mm, 0, getdate()), 0)
declare @hidate datetime; set @hidate = dateadd(mm, 1, @lodate)
select *
from myTable
where datecolumn >= @lodate and datecolumn < @hidate