SELECT * FROM `cover_wid_comments` WHERE `id_group` = 150444045
id_group=150444045
id пользователей это from_id
SELECT `from_id`, COUNT(`from_id`) as 'posts'
FROM `cover_wid_comments`
WHERE DATE_ADD(`date`, INTERVAL 1 DAY) > NOW() AND `id_group`=150444045
GROUP BY `from_id`
ORDER BY count(`from_id`) DESC
LIMIT 1