Number of new contributors (registered contributors per day)

gistfile1.sql

# Shows additions to the groups 'registered as contributors' per day
SELECT DATE(`auth_user`.`date_joined`), count(*) 
FROM `auth_user_groups`
JOIN `auth_user` on `auth_user`.`id`=`auth_user_groups`.`user_id`
WHERE `auth_user_groups`.`group_id` = '45'
AND DATE(`auth_user`.`date_joined`) > '2012-01-01'
GROUP BY DATE(`auth_user`.`date_joined`);