如果不满足交叉连接条件，仍然 return 记录

Question

我有一个 table（姓名：销售）关于客户购买的时间和内容：

Date      C_Name      Thing 
02/21       A         Fruit
02/26       A         Doll
02/27       A         Drink
02/28       B         Book
06/03       B         Fruit
06/13       B         Shoes
06/10       C         Shoes
07/07       A         Tablet
07/11       A         Chair
07/20       A         Sofa
07/21       A         Coat

而且我需要return每个客户每个月购买的前四件商品，如果一个月内购买的商品少于四件，return应该还能看到记录。期望的输出：

Date(Month) C_Name Thing1 Thing2 Thing3 Thing4
2            A     Fruit   Doll   Drink  
2            B     Book
6            B     Fruit   Shoes 
             .  
             . 
             .
7            A     Tablet  Chair  Sofa Coat

我目前的代码如下，只有当客户购买了等于或多于四个物品时才会显示：

SELECT MONTH(s1.Date) AS Date(Month), s1.C_Name, s1.Thing, s2.Thing, s3.Thing, s4.Thing
FROM Sales as s1, Sales as s2, Sales as s3, Sales as s4
ON s1.C_Name = s2.C_Name = s3.C_Name = s4.C_Name
      AND s1.Date<s2.Date 
      AND s2.Date<s3.Date
      AND s3.Date<s4.Date
      AND MONTH(s1.Date) = MONTH(s2.Date)= MONTH(s3.Date)= MONTH(s4.Date);

有什么解决方案可以让我更改我的代码吗？

Answer 1

row_number + pivot

with 
t1 as
(
    select   *, format(Date,'yyyy-MM') as month
    from     Sales
),
t2 as
(
    select  'Thing' 
          + cast(row_number() over 
                  (
                      partition by C_Name, month
                      order by Date
                  ) as varchar(10)
            ) as thing_id
           ,month
           ,C_Name
           ,Thing
    
    from    t1
)
select *
from   t2 pivot (min(Thing) for thing_id in ([Thing1],[Thing2],[Thing3],[Thing4])) as p

month	C_Name	Thing1	Thing2	Thing3	Thing4
2021-02	A	Fruit	Doll	Drink
2021-07	A	Tablet	Chair	Sofa	Coat
2021-02	B	Book
2021-06	B	Fruit	Shoes
2021-06	C	Shoes

Fiddle

如果不满足交叉连接条件，仍然 return 记录

Still return records if unsatisfied cross join condition

sql

sql-server

cross-join