Query a histogram of prices in postgres (number of bis = 20)

histogram-query.sql

SELECT 
  (
    (VALUES ((SELECT max(price/20) FROM prices))) * bin
  )::float AS lower_bin_edge, 
  COALESCE(count, 0) AS count
FROM (
  SELECT 
    floor(
      price / 
      (VALUES ((SELECT max(price/20) FROM prices)))
    ) AS filled_bin, 
    count(*) 
  FROM prices 
  GROUP BY filled_bin
) AS histogram 
RIGHT OUTER JOIN (
  SELECT * FROM generate_series(0,20) AS bin
) AS range
ON (histogram.filled_bin = range.bin);