ORDER BY
    CASE WHEN @OrderBy = 0
    THEN table.id END ASC,
    CASE WHEN @Orderby = 2
    THEN table.id END ASC,

CASE WHEN @OrderBy = 4
THEN (100-((table.price/table.oldprice)*100) as discount END ASC

SELECT * from [table]
ORDER BY
    CASE @OrderBy
        WHEN  0
            THEN [table].id -- ASC
        WHEN 2
            THEN [table].id * -1 -- DESC
    ---I want to do something like below as I don't have discount column in table
        WHEN 4
            THEN (100-([table].price/[table].oldprice)*100)
    END

SELECT *, (100-(table.price/table.oldprice))*100 as discount
FROM table

ORDER BY
CASE WHEN @OrderBy = 0
THEN table.id END ASC,
CASE when @orderby=2
THEN table.id END ASC,
CASE WHEN @OrderBy = 4
THEN discount END ASC

select * from TableName where someCondition >100
  order by
    case when @OrderBy = 'AirlineService'
      then AirlineService END desc,
    case when  @OrderBy = 'SomeMore'
      then  MyOtherColumn  end
GO