Calculat quantile amounts based on aggregate counts. Adapted from https://gist.github.com/hrwgc/5171860

ntile-counts.sql

SELECT
ntile,
avg(ct) AS avgAmount,
max(ct) AS maxAmount,
min(ct) AS minAmount,
median(ct) as median
FROM (SELECT ct, ntile(5) OVER (ORDER BY ct) AS ntile FROM (select count(col_name) as ct from table GROUP BY col_Name) t) x
GROUP BY ntile
ORDER BY ntile;