MySQL自己加入以獲取平均數

Question

如果最近的銷售沒有記錄任何價值，我想根據特定的時間範圍（9到3個月前）找到數據庫中以前記錄的平均值。原因是我們網站上的最近銷售有時不會立即收取佣金，因此我需要回到歷史記錄以找出佣金估算值。計算

佣金率如下：

total_commission/gross_sales 

它是隻需要找出一個估計會是什麼，如果近期的銷售有記錄

這裏沒有「total_commission」是我費了很大的到目前爲止，但我認爲這是錯誤的：

SELECT 
    cs.* 
    ,SUM(cs2.gross_sales) 
    ,SUM(cs2.total_commission) 
    FROM 

    (SELECT 
     sale_id 
    , date 
    , customer_code 
    , customer_country 
    , gross_sales 
    , total_commission 
    FROM customer_sale cs) cs 

    LEFT JOIN customer_sale cs2 
    ON cs2.customer_code = cs.customer_code 
    AND cs2.customer_country = cs.customer_country 
    AND cs2.date > cs.date - interval 9 month 
    AND cs2.date < cs.date - interval 3 month 

    GROUP BY cs.sale_id 

，這樣的數據將被結構如下：

sale_id date   customer_code customer_country gross_sales total_commission 
1  2013-12-01 cust1   united states 10000  1500 
2  2013-12-01 cust2   france   20000  3000 
3  2013-12-01 cust3   united states 15000  2250 
4  2013-12-01 cust4   france   14000  2100 
5  2013-12-01 cust5   united states 13000  1950 
6  2013-12-01 cust6   france   12000  1800 
7  2014-04-02 cust1   united states 10000 
8  2014-04-02 cust2   france   20000 
9  2014-04-02 cust3   united states 15000 
10  2014-04-02 cust4   france   14000 
11  2014-04-02 cust5   united states 13000 
12  2014-04-02 cust6   france   12000 

所以我需要的輸出結果從類似這樣的查詢：（基於同一customer_country 9和3個月前與銷售來自同一customer_code）

sale_id date   customer_code customer_country gross_sales total_commission gross_sales_past total_commission_past 
1  2013-12-01 cust1   united states 10000  1500 
2  2013-12-01 cust2   france   20000  3000 
3  2013-12-01 cust3   united states 15000  2250 
4  2013-12-01 cust4   france   14000  2100 
5  2013-12-01 cust5   united states 13000  1950 
6  2013-12-01 cust6   france   12000  1800 
7  2014-04-02 cust1   united states 10000      10000   1500 
8  2014-04-02 cust2   france   20000      20000   3000 
9  2014-04-02 cust3   united states 15000      15000   2250 
10  2014-04-02 cust4   france   14000      14000   2100 
11  2014-04-02 cust5   united states 13000      13000   1950 
12  2014-04-02 cust6   france   12000      12000   1800 

Answer 1

你的查詢看起來基本上是正確的，但我認爲您的外部查詢需要爲GROUP BY cs.sale_id（假設sale_id在customer_sale表中是唯一的，並且假設date列的數據類型爲DATE，DATETIME或TIMESTAMP）。

我想你想包含一個連接謂詞，這樣你只匹配「過去」行到你沒有總佣金的那些行，

AND cs.total_commission IS NULL 

而我不認爲你真的需要內聯視圖。

---

這就是我想出了：

SELECT cs.sale_id 
    , cs.date 
    , cs.customer_code 
    , cs.customer_country 
    , cs.gross_sales 
    , cs.total_commission 
    , SUM(ps.gross_sales) AS gross_sales_past 
    , SUM(ps.total_commission) AS total_commission_past 
    FROM customer_sale cs 
    LEFT 
    JOIN customer_sale ps 
    ON ps.customer_code = cs.customer_code 
    AND ps.customer_country = cs.customer_country 
    AND ps.date > cs.date - INTERVAL 9 MONTH 
    AND ps.date < cs.date - INTERVAL 3 MONTH 
    AND cs.total_commission IS NULL 
GROUP 
    BY cs.sale_id 

適當的索引可能會提高查詢性能。可能的是，EXPLAIN輸出將顯示「Using temporary; Using filesort」，並且對於大集合來說可能是昂貴的。

MySQL將有可能能夠利用覆蓋索引爲JOIN：

... ON customer_sale (customer_code,customer_country,date,gross_sales,total_commission).