Question

我有一个包含以下两个表的数据库，USERS，POSTS我正在寻找一种方法来计算用户有多少帖子（postCount），以及用户是否有任何帖子postCount将等于零

 Users            Posts
 +----+------+    +----+---------+-----------+
 | ID | Name |    | ID | user_id | Name      |
 +----+------+    +----+---------+-----------+
 | 1  | Bob  |    | 1  | 1       | Blargg... | 
 | 2  | Jim  |    | 2  | 1       | Blargg... | 
 | 3  | Jo   |    | 3  | 2       | Blargg... | 
 +----+------+    +----+---------+-----------+

最后我想要这样的事情：

 +----+------+ 
 | ID | Count|
 +----+------+
 | 1  |  2   |  
 | 2  |  1   |  
 | 3  |  0   |  
 +----+------+

Answer 1

试试这个：

SELECT u.ID, u.Name, COUNT(p.Name)
FROM Users AS u
LEFT JOIN Posts AS p ON u.ID = p.user_id
GROUP BY u.ID, u.Name

Answer 2

SELECT t1.ID, COUNT(*) AS `Count`
FROM Users t1
LEFT JOIN Posts t2
    ON t1.ID = t2.user_id
GROUP BY t1.Id

Answer 3

select
u.id,
count(p.id)
from users u
left join posts p on p.user_id = u.id
group by u.id
order by u.id

Answer 4

你应该加入这两个表，以便包括来自users的所有条目，即使没有用户的帖子，然后是一个简单的order by和一个聚合函数来计算帖子：

select users.id, count(posts.id) from users left join posts on users.id = posts.user_id group by posts.user_id

MySQL QUERY查找每个用户的帖子数量

4 个答案: