多個內部連接 ​​- MySQL的

Question

我有2個表，Task和Transaction，它看起來像這樣：

任務

交易

我想創建一個從兩個表中返回信息的查詢。

色譜柱：name, priority, waiting, error, done, total, status

其中：

• 名稱= Task.name
• 優先= Task.priority
• 等待=計數（transaction.id）WHERE task.id =事務。任務和transaction.status = 1
• error = count（transaction.id）WHERE task.id = transaction.task and transaction.status = 2
• 做=計數（transaction.id）WHERE task.id = transaction.task和transaction.status = 3
• 總=計數（transaction.id）WHERE task.id = transaction.task
• 狀態=任務。狀態

我INNER試圖加入，但我得到一個錯誤的結果：

SELECT tk.name, tk.priority, waiting.waiting, error.error, done.done, total.total 
    FROM task AS tk, transaction AS tran 
    INNER JOIN (
    SELECT count(id) AS waiting 
    FROM transaction 
    WHERE status = 1 
) AS waiting 
    INNER JOIN (
    SELECT count(id) AS error 
    FROM transaction 
    WHERE status = 3 
) AS error 
    INNER JOIN (
    SELECT count(id) AS done 
    FROM transaction 
    WHERE status = 4 
) AS done 
    INNER JOIN (
    SELECT count(id) AS total 
    FROM transaction 
) AS total; 

能否請你幫我創造這個查詢？我得到了等待的列，錯誤，完成，總數與所有交易的計數。相反，它應該獲得交易數量WHERE task.id = transaction.task和transaction.status = 1,2,3。

Answer 1

您現有查詢存在一些問題。首先，你沒有在任何欄目中將你的兩個表格連在一起。看起來你可以加入task.id和transaction.task。第二。你應該能夠通過使用聚合函數一些有條件的邏輯讓每一個總的，就像一個CASE表達式：

SELECT tk.name, tk.priority, 
    sum(case when tran.status = 1 then 1 else 0 end) waiting, 
    sum(case when tran.status = 3 then 1 else 0 end) error, 
    sum(case when tran.status = 4 then 1 else 0 end) done, 
    count(*) total 
FROM task AS tk 
INNER JOIN transaction AS tran 
    ON tk.id = tran.task 
GROUP BY tk.name, tk.priority; 

這種類型的查詢被稱爲一個支點，它就是你從取值您行並將它們轉換成行。在CASE表達式中，您只會得到每個status的總數。

Answer 2

 

    select task.name, 
       task.priority , 
       count(tw.id) as waiting , 
       count(te.id) as error, 
       count(td.id) as done, 
       count(task.id) as total, 
       task.status 
     from transaction as tr 
        JOIN task 
         on task.id = tr.task 
     left JOIN task as tw 
         on (tw.id = tr.task and tr.status = 1) 
     left JOIN task as te 
         on (te.id = tr.task and tr.status = 2) 
     left JOIN task as td 
         on (td.id = tr.task and tr.status = 3) 
     group by task.id 

BY SHAHEN Babayan