Question

我正在尝试计算dellstore2数据库的累计用户数。看看这里和其他论坛的答案，我用了这个

select 
date_trunc('month',orderdate),
sum(count(distinct(customerid)))
   over (order by date_trunc('month',orderdate))
from orders group by date_trunc('month',orderdate)

返回

2004-01-01 00:00:00.0   979
2004-02-01 00:00:00.0   1,952
2004-03-01 00:00:00.0   2,922
2004-04-01 00:00:00.0   3,898
2004-05-01 00:00:00.0   4,873
2004-06-01 00:00:00.0   5,846
2004-07-01 00:00:00.0   6,827
2004-08-01 00:00:00.0   7,799
2004-09-01 00:00:00.0   8,765
2004-10-01 00:00:00.0   9,745
2004-11-01 00:00:00.0   10,710
2004-12-01 00:00:00.0   11,681

每个月都是

看起来总的来说很好，看看前几个项目。但是当我跑了

select count(distinct(customerid)) from orders

对于整个事情，我得到了

与第一个输出11,681中的最后一项不一致。我猜上面的计算不能确定几个月的唯一性。这种计算的最快方法是什么，最好不使用自连接？

Answer 1

您可以使用如下的子查询，而不是直接从订单中选择：

SELECT  OrderDate,
        SUM(COUNT(DISTINCT customerid)) OVER (ORDER BY OrderDate)
FROM    (   SELECT  CustomerID, 
                    DATE_TRUNC('MONTH', MIN(OrderDate)) AS OrderDate
            FROM    Orders
            GROUP BY CustomerID
        ) AS Orders
GROUP BY OrderDate

我认为这可以按要求运作。

http://sqlfiddle.com/#!1/7a8cc/1

修改

如果你仍然需要两种方法（即不同的和正在运行的总数），你可以使用它：

SELECT OrderDate, COUNT(DISTINCT CustomerID) AS MonthTotal, SUM(COUNT(DISTINCT customerid)) OVER (ORDER BY OrderDate) AS CumulativeTotal, SUM(COUNT(DISTINCT CASE WHEN OrderNumber = 1 THEN customerid END)) OVER (ORDER BY OrderDate) AS CumulativeDistinctTotal FROM ( SELECT CustomerID, OrderDate, ROW_NUMBER() OVER(PARTITION BY CustomerID ORDER BY OrderDate) AS OrderNumber FROM Orders ) AS Orders GROUP BY OrderDate

此处示例：

http://sqlfiddle.com/#!1/7a8cc/10

累计每月总计和Postgresql

1 个答案: