如何在Postgresql中显示特定状态下客户和产品的每种组合的最大数量？ [英] How to show the maximum number for each combination of customer and product in a specific state in Postgresql?

问题描述

我刚刚开始学习Postgresql。
我有一个名为 sales的表：

I just begin learning Postgresql recently. I have a table named 'sales':

create table sales
    (
        cust    varchar(20),
        prod    varchar(20),
        day integer,
        month   integer,
        year    integer,
        state   char(2),
        quant   integer
    )

insert into sales values ('Bloom', 'Pepsi', 2, 12, 2001, 'NY', 4232);
insert into sales values ('Knuth', 'Bread', 23, 5, 2005, 'PA', 4167);
insert into sales values ('Emily', 'Pepsi', 22, 1, 2006, 'CT', 4404);
insert into sales values ('Emily', 'Fruits', 11, 1, 2000, 'NJ', 4369);
insert into sales values ('Helen', 'Milk', 7, 11, 2006, 'CT', 210);
......

它看起来像这样：

总共有500行。

It looks like this: And there are 500 rows in total.

现在，我想使用查询来实现这一点：

Now I want to use the query to implement this:

对于客户和产品的每种组合，请分别在3个单独的列中输出
NY的最大销售量以及NJ和CT的最小销售量。与第一个
报告类似，显示相应的日期（即，最大和最小销售
数量的日期）。此外，对于CT和NJ，仅包括2000年以后发生的销售额；纽约的
，包括所有销售额。

应该是这样的：

It should be like this:

我尝试了以下查询：

SELECT
    cust customer,
    prod product,
    MAX(CASE WHEN rn3 = 1 THEN quant END) NY_MAX,
    MAX(CASE WHEN rn3 = 1  THEN TO_DATE(year || '-' || month || '-' || day, 'YYYY-MM-DD') END) date,

    MIN(CASE WHEN rn2 = 1  THEN quant END) NJ_MIN,
    MIN(CASE WHEN rn2 = 1 THEN TO_DATE(year || '-' || month || '-' || day, 'YYYY-MM-DD') END) date,

    MIN(CASE WHEN rn1 = 1  THEN quant END) CT_MIN,
    MIN(CASE WHEN rn1 = 1 THEN TO_DATE(year || '-' || month || '-' || day, 'YYYY-MM-DD') END) date

FROM (
    SELECT
        *,
        ROW_NUMBER() OVER(PARTITION BY cust, prod ORDER BY quant) rn1,
        ROW_NUMBER() OVER(PARTITION BY cust, prod ORDER BY quant) rn2,
        ROW_NUMBER() OVER(PARTITION BY cust, prod ORDER BY quant DESC) rn3

    FROM sales 
) x
WHERE rn1 = 1   OR rn2 = 1   or rn3 = 1 
GROUP BY cust, prod;

结果是：

This is the result:

这是错误的，因为它显示了所有状态的最大数量和最小数量，而不是我想要的特定状态。而且我不知道该如何处理年份这一问题。

This is wrong because it shows me the maximum number and minimum number of all states, not of the specific state I want. And I have no idea how to deal with the year as the question as me to do.

推荐答案

我们可以使用单独的方法进行处理CTE和日历表：

We can handle this using separate CTEs along with a calendar table:

WITH custprod AS (
    SELECT DISTINCT cust, prod
    FROM sales
),
ny_sales AS (
    SELECT *, ROW_NUMBER() OVER (PARTITION BY cust, prod ORDER BY quant DESC) rn
    FROM sales
    WHERE state = 'NY'
),
nj_sales AS (
    SELECT *, ROW_NUMBER() OVER (PARTITION BY cust, prod ORDER BY quant) rn
    FROM sales
    WHERE state = 'NJ'
),
ct_sales AS (
    SELECT *, ROW_NUMBER() OVER (PARTITION BY cust, prod ORDER BY quant) rn
    FROM sales
    WHERE state = 'CT'
)

SELECT
    cp.cust,
    cp.prod,
    nys.quant AS ny_max,
    nys.year::text || '-' || nys.month::text || '-' || nys.day::text AS ny_date,
    njs.quant AS nj_max,
    njs.year::text || '-' || njs.month::text || '-' || njs.day::text AS nj_date,
    cts.quant AS ct_max,
    cts.year::text || '-' || cts.month::text || '-' || cts.day::text AS ct_date
FROM custprod cp
LEFT JOIN ny_sales nys
    ON cp.cust = nys.cust AND cp.prod = nys.prod AND nys.rn = 1
LEFT JOIN nj_sales njs
    ON cp.cust = njs.cust AND cp.prod = njs.prod AND njs.rn = 1
LEFT JOIN ct_sales cts
    ON cp.cust = cts.cust AND cp.prod = cts.prod AND cts.rn = 1
ORDER BY
    cp.cust,
    cp.prod;

注意：您没有提供全面的示例数据，但以上内容似乎在演示中起作用

Note: You didn't provide comprehensive sample data, but the above seems to be working in the demo link below.

< h2>演示

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