This is an example of showing birthdates between 1-nov to 15 dec of this year
select distinct Birthdate from T_staff where Birthdate between cast(cast(11 as varchar)+'-'+cast(1 as varchar)+'-'+cast(year(getdate()) as varchar) as datetime) and cast(cast(12 as varchar)+'-'+cast(15 as varchar)+'-'+cast(year(getdate()) as varchar) as datetime)