Попробуйте этот запрос -
SELECT
DAYOFWEEK(DATE) AS wd,
HOUR(DATE) AS hr,
COUNT(*) AS cnt
FROM
users
GROUP BY
wd, hr
ORDER BY
cnt DESC
SELECT
DATE_FORMAT(DATE, '%a') AS wd, -- or DATE_FORMAT(DATE, '%W')
HOUR(DATE) AS hr,
COUNT(*) AS cnt
FROM
users
GROUP BY
wd, hr
ORDER BY
cnt DESC