MySQL的合併查詢正確

Question

我有一個表來存儲與以下幾列信息：

+----+-----------+-----------+--------------+---------+------+---------------------+---------+ 
| ID | parent_id | author_id | recipient_id | subject | body | created    | is_read | 
+----+-----------+-----------+--------------+---------+------+---------------------+---------+ 
| 1 | 0   | 51  | 52   | sub1 | bod1 | 2017-08-24 15:49:29 | 0 | 
---------------------------------------------------------------------------------------------- 
| 2 | 1   | 52  | 51   | NULL | bod2 | 2017-08-24 15:52:29 | 0 | 
---------------------------------------------------------------------------------------------- 
| 3 | 1   | 51  | 52   | NULL | bod3 | 2017-08-24 15:55:29 | 0 | 
---------------------------------------------------------------------------------------------- 

從這個表，我想提取：每個「線」的

• 的主題 （一個線程的parent_id爲0，對於該主題的回覆具有NULL值）
• 該創建在最近的消息的日期讀
• 在線程未讀消息的數量，其中recipient_id是等於當前USER_ID

例如：

收件人ID 51

+----+-----------+-----------+--------------+ 
| subject | last_message_date_time | unread | 
+----+-----------+-----------+--------------+ 
| sub1 | 2017-08-24 15:55:29 | 1  | 
--------------------------------------------- 

收件人ID 52

+----+-----------+-----------+--------------+ 
| subject | last_message_date_time | unread | 
+----+-----------+-----------+--------------+ 
| sub1 | 2017-08-24 15:55:29 | 2  | 
--------------------------------------------- 

我已經寫了一些個人查詢，但我竭力把他們所有連接在一起（51爲當前用戶ID）：

1.所有線程爲當前用戶（線程具有爲0的PARENT_ID）

SELECT m1.ID, m1.subject 
FROM messages m1 
WHERE (m1.author_id = 51 OR m1.recipient_id = 51) 
    AND m1.parent_id = 0 

2.最後的消息的線程中的時間戳

SELECT MAX(m2.created) as last_message_time_date 
FROM messages m2 
WHERE (author_id = 51 OR recipient_id = 51) 

3.當用戶CURENT不是筆者

SELECT COUNT(m3.ID) as unread 
FROM messages m3 
WHERE recipient_id = 51 
    AND is_read = 0 

我得到儘可能這個未讀郵件數：

SELECT m1.ID, m1.subject, MAX(m2.created), COUNT(m3.ID) 
FROM messages m1 
LEFT JOIN 
    (SELECT created, parent_id 
    FROM messages) AS m2 
    ON m1.ID = m2.parent_id 
LEFT JOIN 
    (SELECT ID, parent_id 
    FROM messages 
    WHERE recipient_id = 51 AND is_read = 0) AS m3 
    ON (m1.ID = m3.parent_id OR m1.ID = m3.ID) 
WHERE (m1.author_id = 51 OR m1.recipient_id = 51) 
    AND m1.parent_id = 0 

我的問題是，計數返回一個不正確的值（超過它應該）。任何建議將不勝感激，非常感謝提前。

Answer 1

如此看來distinct對方回答：

SELECT m1.ID, m1.subject, m2.author_id, MAX(m2.created) as last_message_date_time, COUNT(distinct m3.ID) as unread 
FROM messages m1 

LEFT JOIN messages m2 
    ON (m1.ID = m2.parent_id OR m1.ID = m2.ID) 

LEFT JOIN 
    (
    SELECT ID, parent_id 
    FROM messages 
    WHERE is_read = 0 
     AND recipient_id = 51 
    ) 
    AS m3 
    ON (m1.ID = m3.parent_id OR m1.ID = m3.ID) 

WHERE (m1.author_id = 51 OR m1.recipient_id = 51) 
    AND m1.parent_id = 0 

GROUP BY m1.ID 

仍然是開放的雖然:)