Question

How can I add ELSE clause to the following code?

 ROW_NUMBER() OVER (ORDER BY 
    CASE WHEN @OrderByColumn='ViewCount' AND @OrderDirection=0 THEN docsT.ViewCount END ASC,    
    CASE WHEN @OrderByColumn='AddedDate'AND @OrderDirection=0 THEN docsT.AddedDate END ASC,
    CASE WHEN @OrderByColumn='AddedBy'AND @OrderDirection=0 THEN docsT.AddedBy END ASC,  
    CASE WHEN @OrderByColumn='Title' AND @OrderDirection=0 THEN docsT.Title  END ASC
) AS RowNum

Answer 1

You can put the order in an outer case, and then for selecting the field you can use the form of the case where you compare one value to several values. To support ascending and descending sort, you have to repeat it all again.

order by
  case when @OrderDirection = 0 then
    case @OrderByColumn
      when 'ViewCount' then docsT.ViewCount
      when 'AddedDate' then docsT.AddedDate
      when 'AddedBy' then docsT.AddedBy
      when 'Title' then docsT.Title
      else docsT.Title
    end
  end asc,
  case when @OrderDirection = 1 then
    case @OrderByColumn
      when 'ViewCount' then docsT.ViewCount
      when 'AddedDate' then docsT.AddedDate
      when 'AddedBy' then docsT.AddedBy
      when 'Title' then docsT.Title
      else docsT.Title
    end
  end desc