MySQL查詢找到每個用戶的帖子數

Question

我有一個數據庫與下面的兩個表，用戶，POSTS我正在尋找一種方法來獲得有多少職位（postCount）的用戶有計數，如果一個用戶沒有任何職位postCount將等於零

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

最後，我想是這樣的：

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

Answer 1

試試這個：

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

你應該離開加入了兩個表，以包括來自users所有條目，即使沒有帖子的用戶，那麼一個簡單的ORDER BY和集合函數來計算的職位：

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