是否可以有条件地 select 基于 MySQL 中另一列的值的列值

Question

我有一个查询，我使用 CTE 从一个巨大的表中获取数据并从记录中聚合值，然后使用查询来进一步处理我拥有的数据。 我的表看起来与此类似

CREATE TABLE `fact_data` (
  `product` varchar(20),
  `location` varchar(20),
  `month` varchar(20),
  `sales` bigint(20) DEFAULT 0,
  `discount` bigint(20) DEFAULT 0
);

INSERT INTO table
(product, location, month, sales, discount) VALUES('P1','L1','Jan',104,5);
INSERT INTO table
(product, location, month, sales, discount) VALUES('P1','L2','Jan',88,10);
INSERT INTO table
(product, location, month, sales, discount) VALUES('P1','L3','Jan',97,15);
INSERT INTO table
(product, location, month, sales, discount) VALUES('P1','L4','Jan',106,5);
INSERT INTO table
(product, location, month, sales, discount) VALUES('P1','L5','Jan',108,10);
INSERT INTO table
(product, location, month, sales, discount) VALUES('P1','L6','Jan',117,5);
INSERT INTO table
(product, location, month, sales, discount) VALUES('P1','L1','Feb',85,5);
INSERT INTO table
(product, location, month, sales, discount) VALUES('P1','L2','Feb',116,10);
INSERT INTO table
(product, location, month, sales, discount) VALUES('P1','L3','Feb',89,15);
INSERT INTO table
(product, location, month, sales, discount) VALUES('P1','L4','Feb',92,5);
INSERT INTO table
(product, location, month, sales, discount) VALUES('P1','L5','Feb',98,10);
INSERT INTO table
(product, location, month, sales, discount) VALUES('P1','L6','Feb',119,15);
INSERT INTO table
(product, location, month, sales, discount) VALUES('P1','L7','Feb',112,10);

我使用的查询是这样的。

    WITH t AS (
    SELECT
       Month,
       SUM(Sales) as Sales,
       AVG(Discount) as Discount
       from table
    WHERE
       Product = 'P1'
    GROUP BY Month
    )
    Select * from t

现在，我想获得每月出现在该产品的最大商店数中的折扣。 我想要的有效结果如下，因为我希望在所有商店中添加产品的销售额，因此 1 月份为 620，但显示 5 为折扣，因为它在 1 月份在大多数商店都可用。

Answer 1

尝试这个：

WITH Level1 AS (
    select count(*) as CountOfDiscount, month, discount 
    from fact_data 
    group by month, discount
),
Level2 AS (
    SELECT Month, Discount
    FROM Level1 
    WHERE CountOfDiscount = (SELECT MAX(CountOfDiscount) FROM Level1 AS A WHERE 
       A.Month = Level1.Month)
   )
SELECT Level2.Month, SUM(Sales) AS SumOfSales, Level2.Discount
FROM Level2 
JOIN fact_data 
ON Level2.Month = fact_data.Month
GROUP BY LEvel2.Month, Level2.Discount