I want to get one value from a function using a case expression. I tried the following but it does not work:

CREATE FUNCTION [FATMS].[fnReturnByPeriod]
(       
    @Period INT     
)
RETURNS int
AS
BEGIN

    select case @Period 
             when 1 then 1
             when @Period >1 and @Period <=7 then 1
             when @Period >7 and @Period <=30 then 1
             when @Period >30 and @Period<=90 then 1
             when @Period >90 and @Period <=180 then 1
             when @Period >180 and @Period <=360 then 1
             else 0
           end
    
    return @Period
END