客户每月的 SQL 平均值

Question

“交易”表是所有交易的列表，其中包含日期、客户ID、单位成本(价格)和数量。

我需要一份报告，将交易按月份分组并给出计数、总收入和每个客户的平均收入。

我无法弄清楚如何将 group by customerID 插入此选择语句:

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:

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);

但在我思考了一分钟后，这种方法就不再有意义了，因为嵌套的 select 将返回多行。如果我添加一个 where 子句并在第二个选择中删除 group by date:

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

然后它会返回...我不确定是什么，但这是错误的。

顺便说一句，这是一个 Oracle 数据库(我认为是 10g)。

Answer 1

您可以使用算术来完成此操作。 。 。将总数除以客户数量:

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);