Indexing to reduce cost of SORT - tsql

Question

I have this table:
TopScores
Username char(255)
Score int
DateAdded datetime2
which will have a lot of rows.
I run the following query (code for a stored procedure) against it to get the top 5 high scorers, and the score for a particular Username preceded by the person directly above them in position and the person below:
WITH Rankings
AS (SELECT Row_Number() OVER (ORDER BY Score DESC, DateAdded DESC) AS Pos,
--if score same, latest date higher
Username,
Score
FROM TopScores)
SELECT TOP 5 Pos,
Username,
Score
FROM Rankings
UNION ALL
SELECT Pos,
Username,
Score
FROM Rankings
WHERE Pos BETWEEN (SELECT Pos
FROM Rankings
WHERE Username = #User) - 1 AND (SELECT Pos
FROM Rankings
WHERE Username = #User) + 1
I had to index the table so I added clustered: ci_TopScores(Username) first and nonclustered: nci_TopScores(Dateadded, Score).
Query plan showed that clustered was completely ignored (before I created the nonclustered I tested and it was used by the query), and logical reads were more (as compared to a table scan without any index).
Sort was the highest costing operator. So I adjusted indexes to clustered: ci_TopScores(Score desc, Dateadded desc) and nonclustered: nci_TopScores(Username).
Still sort costs the same. Nonclustered: nci_TopScores(Username) is completely ignored again.
How can I avoid the high cost of sort and index this table effectively?

Answer 1

The CTE does not use Username so not a surprise it does not use that index.
A CTE is just syntax. You are evaluating that CTE 4 times.
Try a #temp so it is only evaluated once.
But you need to think about the indexes.
I would skip the RowNumber and just put an iden pk on the #temp to serve as pos
I would skip any other indexes on #temp
For TopScores an index on Score desc, DateAdded desc, Username asc will help
But it won't help if it is fragmented
That is an index that will fragment when you insert
insert into #temp (Score, DateAdded, Username)
select Score, DateAdded, Username
from TopScores
order by Score desc, DateAdded desc, Username asc
select top 5 *
from #temp
order by pos
union
select three.*
from #temp
join #temp as three
on #temp.UserName = #user
and abs(three.pos - #temp.pos) <= 1
So what if there is table scan on #temp UserName.
One scan does not take as long as create one index.
That index would be severely fragmented anyway.