Q&A for power users of web applications
SELECT AVG(reputation), stdev(reputation)
FROM (SELECT u.id as uid, COUNT(p.id) as nbAns
FROM Users as u
INNER JOIN Posts as p ON p.OwnerUserId = u.id
WHERE PostTypeId = 2 and p.CreationDate > '2016-04-01'
GROUP BY u.id) as countAns
INNER JOIN Users AS u on u.id = countAns.uid