rails COUNT SELECT DISTINCT

Question

我正在记录用户观看一系列视频的次数.现在,我正在尝试制作每天观看任何视频的用户数量的图表.

UserVideoWatching.where("created_at >= ? AND user_id != ?",1.month.ago, User.elephant.id).group("DATE(created_at)").reorder('created_at').count

生成sql

SELECT COUNT(*) AS count_all, DATE(created_at) AS date_created_at FROM `user_video_watchings` WHERE (created_at >= '2013-01-27 10:43:24' AND user_id != 7) GROUP BY DATE(created_at) ORDER BY created_at

这会为每天观看的所有视频产生正确的结果,但正如我所说,我只想向每位用户展示一次.

我想要的sql是

SELECT COUNT(DISTINCT user_id) AS count_all, DATE(created_at) AS date_created FROM `user_video_watchings` WHERE (created_at >= '2013-01-27 10:33:18' AND user_id != 7) GROUP BY DATE(created_at) ORDER BY created_at

所以我认为

UserVideoWatching.where("created_at >= ? AND user_id != ?",1.month.ago, User.elephant.id).group("DATE(created_at)").reorder('created_at').select('COUNT(DISTINCT user_id) AS count_all, DATE(created_at) AS date_created')

会做我想做的事.但这给了

[#<UserVideoWatching >, #<UserVideoWatching >]

而不是哈希.

有任何想法吗？

我正在使用rails 3.1和mysql

Answer 1

你可以用distinct.count(:attribute_name).

(在Rails 3中使用:count(:user_id, distinct: true)代替)

从而:

UserVideoWatching.where("created_at >= ? AND user_id != ?", 1.month.ago, User.elephant.id)
.group("DATE(created_at)").reorder('created_at').distinct.count(:user_id)

无法测试,但我认为这将产生你想要的SQL.

Answer 2

在Rails 4中,使用(...).uniq.count(:user_id)其他答案中提到的(对于此问题和SO上的其他内容)实际上会导致DISTINCT查询中出现额外的问题:

SELECT DISTINCT COUNT(DISTINCT user_id) FROM ...

我们实际需要做的是自己使用SQL字符串:

(...).count("DISTINCT user_id")

这给了我们:

SELECT COUNT(DISTINCT user_id) FROM ...