查找每个类别中最畅销的 3 种产品

Question

我正在尝试查找每个类别中最畅销的 3 种产品。但是我尝试的 SQL 并没有产生正确的结果。这是我做的事情：

产品表：

CREATE TABLE [dbo].[Products](
    [id] [int] IDENTITY(1,1) NOT NULL,
    [name] [nvarchar](100) NOT NULL,
    [category] [nvarchar](100) NOT NULL,
 CONSTRAINT [PK_Products] PRIMARY KEY CLUSTERED 
(
    [id] ASC
)

id	name	category
1	prod1	cat1
2	prod2	cat1
3	prod3	cat1
4	prod4	cat1
5	prod5	cat1
6	prod6	cat2
7	prod7	cat2
8	prod8	cat2
10	prod10	cat2

OrderItems 表：

CREATE TABLE [dbo].[OrderItems](
    [id] [int] IDENTITY(1,1) NOT NULL,
    [prodID] [int] NOT NULL,
    [quantity] [int] NOT NULL,
 CONSTRAINT [PK_OrderItems] PRIMARY KEY CLUSTERED 
(
    [id] ASC
)

ALTER TABLE [dbo].[OrderItems]  WITH CHECK ADD  CONSTRAINT [FK_OrderItems_Products] FOREIGN KEY([prodID])
REFERENCES [dbo].[Products] ([id])

ALTER TABLE [dbo].[OrderItems] CHECK CONSTRAINT [FK_OrderItems_Products]

id	prodID	quantity
1	1	10
2	2	6
3	2	6
4	4	3
5	3	2
6	6	10
7	7	1

我试过的 SQL：

select *
from (select p1.id, p1.category, (select sum(quantity) from OrderItems as oi where oi.prodID = p1.id) as sales
from Products as p1) as p2
where p2.sales >= (
    select distinct(sales)
    from (select p1.id, p1.category, (select sum(quantity) from OrderItems as oi where oi.prodID = p1.id) as sales
from Products as p1) as p3
    where p2.category = p3.category
    order by sales desc
    offset 2 rows fetch next 1 rows only)

预期结果：

id	category	sales
1	cat1	10
2	cat1	12
4	cat1	3
6	cat2	10
7	cat2	1

实际结果：

id	category	sales
1	cat1	10
2	cat1	12
4	cat1	3

查询中有什么错误？有没有更好的方法来达到这个结果？

Answer 1

您可以加入表格并汇总以获取每种产品的总销售额。
还可以使用ROW_NUMBER()窗口函数根据产品的类别和总销售额排序来对每个产品进行排名和过滤：

SELECT id, category, sales
FROM (
  SELECT p.id, 
         MAX(category) category, 
         SUM(o.quantity) sales,
         ROW_NUMBER() OVER (PARTITION BY MAX(category) ORDER BY SUM(o.quantity) DESC) rn
  FROM Products p INNER JOIN OrderItems o
  ON o.prodID = p.id
  GROUP BY p.id
) t
WHERE rn <= 3
ORDER BY id;

或者，先在OrderItems聚合，然后加入：

SELECT id, category, sales
FROM (
  SELECT p.id, 
         p.category, 
         o.sales,
         ROW_NUMBER() OVER (PARTITION BY p.category ORDER BY o.sales DESC) rn
  FROM Products p 
  INNER JOIN (
    SELECT prodID, SUM(quantity) sales
    FROM OrderItems
    GROUP BY prodID
  ) o ON o.prodID = p.id
) t
WHERE rn <= 3
ORDER BY id;

请参阅demo。