如何在 Postgresql 中显示特定状态下每个客户和产品组合的最大数量？

Question

我最近才开始学习Postgresql。我有一个名为 'sales':

的 table

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);
......

看起来像这样：总共有500行。

现在我想使用查询来实现这个：

对于客户和产品的每个组合，输出最大销售数量纽约州和新泽西州和康涅狄格州的最低销售数量在 3 个单独的列中。像第一个报告，显示相应的日期（即那些最大和最小销售额的日期数量）。此外，对于 CT 和 NJ，仅包括 2000 年之后发生的销售额；对于纽约，包括所有销售额。

应该是这样的：

我试过以下查询：

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;

这是结果：

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。而且我不知道如何处理年份作为我的问题。

Answer 1

我们可以使用单独的 CTE 和日历来处理这个问题 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，但上面的内容似乎在下面的演示中有效 link。

如何在 Postgresql 中显示特定状态下每个客户和产品组合的最大数量？

How to show the maximum number for each combination of customer and product in a specific state in Postgresql?

postgresql

join

group-by

row-number

case-when

Demo