Question

I have the following select SQL that does a basic select statement although it does include a calculated column:

    Select *
    From
    (
      Select *,
             ROW_NUMBER() OVER
                              (ORDER BY
                                CASE WHEN @sortBy = 0 THEN R.DateCreated End Desc,
                                CASE WHEN @sortBy = 1 THEN R.DateCreated end Asc,
                                CASE WHEN @sortBy = 2 THEN TotalVotes END Desc,
                                CASE WHEN @sortBy = 2 THEN R.TotalFoundNotUseful END Desc
                              ) AS RowNumber 

      From
      (
        Select *, (TotalFoundUseful + TotalFoundNotUseful) As TotalVotes
      From Reviews
      Where (DealID = @dealID) And (TotalAbuses < 10) And (Deleted = 0)
    ) As R
  ) As Rev
  Where RowNumber BETWEEN @startRecord AND @endRecord

If you look carefully, the SELECT statement itself is executed 3 times. I can’t believe that this is necessary. Is there a way to reduce this to 2 select statements (or possibly even one). I don’t actually need to return the RowNumber. It is only used for selecting rows within a certain range.

Answer 1

You can do it with two by putting the rownumber in with the original select against reviews. You can’t go to one if you want to have a WHERE clause on a windowing function like ROW_NUMBER.

You do have to write TotalFoundUseful + TotalFoundNotUseful twice but it will only be evaluated once so that doesn’t effect performance.

I also wouldn’t expect moving to two to have any effect on performance but you should test it.

Select *
    From
    (
  Select *, (TotalFoundUseful + TotalFoundNotUseful) As TotalVotes,
          ROW_NUMBER() OVER
              (ORDER BY
            CASE WHEN @sortBy = 0 THEN DateCreated End Desc,
            CASE WHEN @sortBy = 1 THEN DateCreated end Asc,
            CASE WHEN @sortBy = 2 THEN TotalFoundUseful + TotalFoundNotUseful END Desc,
            CASE WHEN @sortBy = 2 THEN TotalFoundUseful END Desc
          ) AS RowNumber 
 From Reviews
     Where (DealID = @dealID) And (TotalAbuses < 10) And (Deleted = 0)

  ) As Rev
  Where RowNumber BETWEEN @startRecord AND @endRecord