获得前N对产品，客户通常购买

Question

我面临着返回前N对产品的问题，即客户购买的共同点。让说，我有以下查询：

SELECT c.CustomerKey, ProductAlternateKey 
FROM 
    [AdventureWorksDW2008R2].[dbo].[FactInternetSales] FIS JOIN 
    dbo.DimCustomer C ON C.CustomerKey = FIS.CustomerKey JOIN 
    dbo.DimProduct P ON P.ProductKey = FIS.ProductKey 

GROUP BY 
    C.CustomerKey, P.ProductAlternateKey 

，并返回结果如下：

CustomerKey | ProductAlternateKey| 
-------------+-----------+ 
0001   | A     | 
0001   | B     | 
0002   | A     | 
0002   | B     | 
0002   | C     | 
0003   | B     | 
0003   | C     | 
0004   | A     | 
0004   | B     | 
0005   | A     | 
0005   | C     | 

从这个查询我想找到顶部2对客户买，所以在我的例子产品 - >（A，B）出现3次，（B，C）→出现2次

Answer 1

这给测试：

declare @Orders table (OrderID int identity, PersonID int, Description varchar(32), ProductId int, Amount int); 

insert into @Orders values (1, 'Shirt', 1, 20),(1, 'Shoes', 2, 50),(2, 'Shirt', 1, 22),(2, 'Shoes', 2, 20),(3, 'Shirt', 1, 20),(3, 'Shoes', 2, 50),(3, 'Hat', 3, 20),(4, 'Shirt', 1, 20),(5, 'Shirt', 1, 20),(5, 'Pants', 4, 30),(6, 'Shirt', 1, 20),(6, 'RunningShoes', 5, 70),(6, 'Hat', 3, 20),(7, 'Shirt', 1, 22),(7, 'Shoes', 2, 40),(7, 'Coat', 6, 80); 

select 
    top 2  
    I.Description, 
    M.Description 
from @Orders as I 
inner join @Orders as C on C.ProductId = I.ProductId and C.PersonId <> I.PersonId 
inner join @Orders as M on C.PersonId = M.PersonId and C.ProductId <> M.ProductId 
where 
    I.productid = 3 
    and I.ProductId<>M.ProductId 
group by 
    I.Description 
    ,M.Description 
order 
    by count(2) desc 

Answer 2

使用RANK或DENSERANK函数。 MSDN上排名功能：http://msdn.microsoft.com/en-us/library/ms176102.aspx

用法示例与自我解压的SQL：

declare @Person Table (personID int identity, person varchar(8)); 

insert into @Person values ('Brett'),('Sean'),('Chad'),('Michael'),('Ray'),('Erik'),('Queyn'); 

declare @Orders table (OrderID int identity, PersonID int, Desciption varchar(32), Amount int); 

insert into @Orders values (1, 'Shirt', 20),(1, 'Shoes', 50),(2, 'Shirt', 22),(2, 'Shoes', 20),(3, 'Shirt', 20),(3, 'Shoes', 50),(3, 'Hat', 20),(4, 'Shirt', 20),(5, 'Shirt', 20),(5, 'Pants', 30), 
(6, 'Shirt', 20),(6, 'RunningShoes', 70),(7, 'Shirt', 22),(7, 'Shoes', 40),(7, 'Coat', 80); 

with a as 
    (
    Select 
     person 
    , o.Desciption 
    , o.Amount 
    , rank() over(partition by p.personId order by Amount) as Ranking 
    , Dense_rank() over(partition by p.personId order by Amount) as DenseRanking 
    from @Person p 
     join @Orders o on p.personID = o.PersonID 
    ) 
select * 
from a 
where Ranking <= 2 -- determine top 2, 3, etc.... whatever you want. 
order by person, amount