Group by every N records in T-SQL

Question

I have some performance test results on the database, and what I want to do is to group every 1000 records (previously sorted in ascending order by date) an

Answer 1

WITH T AS (
  SELECT RANK() OVER (ORDER BY ID) Rank,
    P.Field1, P.Field2, P.Value1, ...
  FROM P
)
SELECT (Rank - 1) / 1000 GroupID, AVG(...)
FROM T
GROUP BY ((Rank - 1) / 1000)
;

Something like that should get you started. If you can provide your actual schema I can update as appropriate.