[英]SQL select query about grouping 2 columns
I am trying to get my head around this query - seems pretty straight forward 我试图了解这个问题 - 看起来非常简单
The table below captures which user watched which video 下表显示了哪个用户观看了哪个视频
topic_user_id | topic_id | user_id 1 | 10 | 3 2 | 10 | 4 3 | 11 | 5 4 | 11 | 3 5 | 12 | 6 6 | 13 | 6 7 | 14 | 7 8 | 11 | 8 9 | 11 | 9 10 | 14 | 10 11 | 15 | 11 12 | 16 | 11 13 | 17 | 11
Now to find out how many users watched a particular video - I have the following query. 现在,要了解有多少用户观看了特定视频 - 我有以下查询。
HOW MANY USERS HAVE WATCHED A PARTICULAR VIDEO
有多少用户观看了一个特别的视频
select count(distinct(user_id)) as 'Number of Users',topic_id from topic_user where user_id is not null group by topic_id
Output 产量
Number of Users | topic_id 2 | 10 4 | 11 1 | 12 1 | 13 2 | 14 1 | 15 1 | 16 1 | 17 Read as: 2 users watched topic 10 , 4 watched topic 11 and so on
This works fine - But what I am looking for is to find : 这很好 - 但我要找的是找到:
How many users watched 1 video
有多少用户观看了1个视频
How many users watched 2 videos
有多少用户观看了2个视频
How many users watched 3 videos
有多少用户观看了3个视频
The output should be something like 输出应该是这样的
Number of Users | Number of Videos watched 6 | 1 2 | 2 1 | 3 Read as - 6 people watched only 1 video, 2 people watched 2 videos and so on.
Need some help with this. 需要一些帮助。
Thanks in advance 提前致谢
There may be an easier way but a subquery will work 可能有一种更简单的方法,但子查询将起作用
select
videos as 'Number of videos',
count(user_id) as 'Num of Users'
from (
select
count(distinct(topic_id)) as videos,
user_id from topic_user
group by
user_id
) sub
group by
videos
select u.n as `Number of Video watched`, count(t.user_id)
from
(select user_id, count(*) as `cnt`
from topic_user
group by user_id) t INNER JOIN(
SELECT 1 as `n` FROM DUAL
UNION
SELECT 2 as `n` FROM DUAL
UNION
SELECT 3 as `n` FROM DUAL) u ON u.n = t.cnt
group by u.n
Fiddle: http://sqlfiddle.com/#!2/844ee/15 小提琴: http ://sqlfiddle.com/#!2/844ee/15
Try this:: 尝试这个::
Select first_table.count(distinct(user_id)) as 'Number of Users', SUM(Count(topic_id))
from
(select count(distinct(user_id)) as 'Number of Users',topic_id from topic_user
where user_id is not null
group by topic_id) as first_table group by Count(topic_id)
Try this 试试这个
SELECT videos AS `Number of videos`,COUNT(user_id) AS `Num of Users`
FROM (SELECT COUNT(DISTINCT(topic_id)) AS videos,user_id FROM topic_user
GROUP BY user_id) sub_query
GROUP BY
videos
"How many users watched n videos" could be interpreted two ways: “观看n个视频的用户数量”可以通过两种方式解释:
1) How many users watched n videos, regardless of title? 1)有多少用户观看了n个视频,无论标题是什么? The same video title may have been watched twice.
可能已经观看了两次相同的视频标题。
select videoCount, count(*) as userCount
from (
select count(*) as videoCount
from topic_user
group by user_id
) t
group by videoCount
2) How many users watched n different video titles. 2)有多少用户观看了不同的视频节目。
select videoCount, count(*) as userCount
from (
select count(distinct topic_id) as videoCount
from topic_user
group by user_id
) t
group by videoCount
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