题解 | #牛客每个人最近的登录日期(四)#

SELECT l.`date`,count(temp.u_id) FROM 
-- 去重日期
(SELECT DISTINCT date FROM login) l
LEFT JOIN 
-- 新增用户记录
(SELECT l.`date`,l.user_id u_id FROM login l
WHERE NOT EXISTS (
	SELECT 1 FROM login l2
	WHERE l.user_id = l2.user_id
	AND l.`date` > l2.`date`
)) temp
ON l.date = temp.date
GROUP BY l.date