Question

我现在约20分钟一直在努力，尽管我可能会在这里得到一些帮助。我有两张桌子，以多对一的关系。用户（一）和事件（很多）。简化的表格如下所示：

users
-----------
user_id
group_id

events
-----------
user_id

我正在尝试生成一个报告，该报告将显示每个组至少有一个事件的用户数。所以结果集有望看起来像：

group_id   users_with_at_least_one_event
1          689
2          312

Answer 1

SELECT  group_id, count(*) users_with_at_least_one_event
FROM 
(
SELECT  u.user_id, u.group_id, count(*) as event_count
FROM    users u
        JOIN events e
        ON u.user_id = e.user_id
GROUP BY u.user_id, u.group_id
HAVING count(*) > 1
) sub
GROUP BY group_id

Answer 2

尝试

select users.group_id, count(distinct users.user_id) as users_with_at_least_one_event
from 
users, events 
where users.user_id = events.user_id 
group by users.group_id

Answer 3

SELECT users.group_id, COUNT(*) FROM users 
WHERE users.user_id IN (SELECT events.user_id FROM events)

Answer 4

SELECT group_id, COUNT(users.user_id) AS users_with_at_least_one_event,
FROM users, events
WHERE users.user_id = events.user_id
GROUP BY group_id

可能？

由总数（mySQL）的组选择

4 个答案: