calculating equal frequency buckets, or n-tile ranges in postgresql

n-tile.sql

-- To calculate flexible quantile ranges in postgresql, for example to calculate n equal 
-- frequency buckets for your data for use in a visualisation (such as binning for a 
-- choropleth map), you can use the following SQL:

-- this functions returns 6 equal frequency bucket ranges for my_column.
SELECT ntile, avg(my_column) AS avgAmount, max(my_column) AS maxAmount, min(my_column) AS minAmount 
FROM (SELECT my_column, ntile(6) OVER (ORDER BY my_column) AS ntile FROM my_table) x
GROUP BY ntile ORDER BY ntile

-- more on the ntile() function and windowing here: 
-- http://database-programmer.blogspot.com/2010/11/really-cool-ntile-window-function.html