計數的MySQL GROUP BY

Question

所以，我有一個表結構：

有沒有一種方法，使SQL查詢計數呈三角哈希在r_hash列，比創立這個散列hash列，並返回一個uid和哈希計數？

例如 - uid - 21520578;類型 - 1;數 - 7？

Answer 1

嘗試下面的查詢

SELECT T1.uid, T1.type, T2.count 
FROM table T1, 
(
    SELECT r_hash, COUNT(*) AS count 
    FROM table 
    GROUP BY r_hash 
) T2 
WHERE T1.hash = T2.r_hash 

Answer 2

你可以通過使用連接

SELECT t1.uid, t1.type, COUNT(t2.id) as `count` 
FROM table AS t1 
LEFT JOIN table AS t2 ON t2.r_hash = t1.hash 
GROUP BY t1.id 

我沒有測試此查詢。

編輯：左加入你也算收到行= 0