SELECT `uid`,
COUNT(CASE WHEN DATE(`start`) >= CURDATE() AND `end`>0 THEN 1 END) AS `total_day`,
COUNT(CASE WHEN DATE(`start`) >= DATE_SUB(CURDATE(),INTERVAL 7 DAY) AND `end`>0 THEN 1 END) AS `total_week`,
COUNT(CASE WHEN `end`>0 THEN 1 END) AS `total_month`,
CASE WHEN `end`=0 THEN DATE_FORMAT(`start`,'%H:%i') END AS `active_meeting`
--      (SELECT DATE_FORMAT(`start`,'%H:%i') FROM `meetings` WHERE `uid`=t1.`uid` AND `start`>0 AND `end`=0) AS `active_meeting`
FROM `meetings` AS `t1`
WHERE `start` >= DATE_SUB(CURDATE(),INTERVAL 30 DAY)
GROUP BY `uid` ORDER BY `total_month` DESC;

MAX(CASE `end`=0 THEN `start` END)