create function getNote (@score int) 
returns nvarchar(4) 
as
begin
	declare @note nvarchar(4)

	if @score between 0 and 50 
		set @note = 'Half'
	else
		set @note = 'Full'

	return @note
end

--Test case
create table #exam 
(
	e_id int identity(1,1) primary key,
	e_score int,
	e_note nvarchar(4)
)

insert into #exam(e_score, e_note) 
values (51, dbo.getNote(51)) 

insert into #exam(e_score, e_note) 
values (50, dbo.getNote(50)) 

select * from #exam

drop table #exam

e_id        e_score     e_note 
----------- ----------- ------ 
1           51          Full
2           50          Half