SQL to find active contributors as of 20140401

active_contributors.sql

SELECT COUNT(*) 
  FROM (
    SELECT user_name, COUNT(*) AS months
      FROM (
        SELECT DISTINCT user_name, date_trunc('month', created_at) as mon 
          FROM osm_changeset 
          WHERE num_changes > 0 
            AND created_at BETWEEN '20130401'::date AND '20140401'::date) 
        AS um GROUP BY user_name) 
    AS mon 
  WHERE months >= 3;