ntile truncated mean

/* AVG */
-- AVG(Rate) OVER (PARTITION BY group_Id) AS AvgRate
-- 2  89,9090909090909
-- 3  58,3333333333333

/* NTILE */
WITH truncatedSet AS (SELECT Rate, ntile(10) OVER(ORDER BY Rate) AS n FROM RateCalculatorLookups WHERE rate IS NOT NULL AND group_id = 3)
SELECT * FROM truncatedSet
-- 50   1   -- gets removed
-- 50   2
-- 50   3
-- 50   4
-- 50   5
-- 100  6   -- should be removed

SELECT avg(Rate) FROM truncatedSet WHERE n BETWEEN 2 AND 19
-- 60