Ratio when using group by

example.sql

-- Compute the ratios of each type of status from the overall count
-- After re-learning it over and over again, it is time to document this useful snippet.
-- I hope my future-self will find it.

SELECT status,
       c,
       c / cast((sum(c) over ()) AS float) AS ratio
FROM
  (SELECT status,
          count(*) AS c
   FROM table
   WHERE cond1 = 1
     AND date_foo < '2017-01-01'
     AND date_foo < '2016-09-30'
   GROUP BY status) AS f