客戶每月的SQL平均值

Question

該表的「交易」是所有具有date,customerID，單位成本（price）和quantity的交易的列表。

我需要一份報告，將交易分組爲幾個月，並給出計數，總收入和每位客戶的平均收入。

我無法搞清楚如何將group by customerID這個select語句：

SELECT extract(month FROM date) month, 
     count(*) purchases, 
     SUM(price*quantity) income, 
     AVG(SUM(price*quantity)) <-- this needs to be grouped by customerID aswell as month 
FROM 
    transactions 
WHERE 
    date BETWEEN i2 AND i3 
GROUP BY extract(month FROM date); 

我能得到的最接近的是一樣的東西：

SELECT extract(month FROM date) month, 
     count(*) purchases, 
     SUM(price*quantity) income, 
     (SELECT AVG(SUM(price*quantity)) 
     FROM transactions 
     GROUP BY customerID, extract(month FROM date)) 
FROM 
    transactions t 
WHERE 
    date BETWEEN i2 AND i3 
GROUP BY extract(month FROM date); 

但這種方法停止決策意識後我想了一會兒，因爲嵌套的select會返回多行。如果我添加一個where條款，並刪除在第二個group by date選擇：

(SELECT AVG(SUM(price*quantity)) 
FROM transactions 
GROUP BY customerID 
where extract(month FROM date) = month) 

然後，它會返回...我不知道，但它是錯誤的。

這是一個oracle數據庫的方式（我認爲是10g）。

Answer 1

您可以使用算術做到這一點。 。 。除以客戶總數：

SELECT extract(month FROM date) month, 
     count(*) purchases, 
     SUM(price*quantity) income, 
     sum(price*quantity)/count(distinct customerId) 
FROM 
    transactions 
WHERE 
    date BETWEEN i2 AND i3 
GROUP BY extract(month FROM date);