在 sql 服务器 2012 中查找最频繁的值

Question

我想找到每个客户购买频率最高的产品。我的数据集是这样的：

CustomerID     ProdID    FavouriteProduct
    1              A              ?
    1              A              ?
    1              A              ?
    1              B              ?
    1              A              ?
    1              A              ?
    1              A              ?
    1              B              ?
    2              A              ?
    2              AN             ?
    2              G              ?
    2              C              ?
    2              C              ?
    2              F              ?
    2              D              ?
    2              C              ?

产品太多，所以我不能把它们放在一个枢轴上table。

答案如下所示：

CustomerID     ProdID    FavouriteProduct
    1              A              A
    1              A              A
    1              A              A
    1              B              A
    1              A              A
    1              A              A
    1              A              A
    1              B              A
    2              A              C
    2              AN             C
    2              G              C
    2              C              C
    2              C              C
    2              F              C
    2              D              C
    2              C              C

查询可能如下所示：

Update table
set FavouriteProduct = (Select 
                            CustomerID, Product, Max(Count(Product)) 
                        From Table 
                        group  by CustomerID, Product) FP

Answer 1

感谢 Nick，我找到了一种查找最频繁值的方法。我与你分享它是如何工作的：

   Select CustomerID,ProductID,Count(*) as Number 
   from table A 
   group by CustomerID,ProductID 
   having Count(*)>= (Select Max(Number) from (Select CustomerID,ProductID,Count(*) as Number from table B where B.CustomerID= A.CustomerID  group by CustomerID,Product)C)

Answer 2

以防万一您的 SQL 执行速度不够快并且您的客户也在较小的 table 中，这可能会更好::

select C.CustomerId, R.ProductID
from Customer C
outer apply (
  Select top 1 ProductID,Count(*) as Number 
  from table A 
  where A.CustomerId = C.CustomerId
  group by ProductId
  order by Number desc 
) R

Answer 3

获得最频繁产品的另一种方法是使用 row_number():

select customerid, productid,
       max(case when seqnum = 1 then productid end) over (partition by customerid) as favoriteproductid
from (select customerid, productid, count(*) as cnt,
             row_number() over (partition by customerid order by count(*) desc) as seqnum
      from customer c
      group by customerid, productid
     ) cp;

Answer 4

这个基于本页末尾的示例：http://www.sql-server-performance.com/2006/find-frequent-values/ 可能更快：

SELECT CustomerID, ProdID, Cnt 
FROM 
(
    SELECT CustomerID, ProdID, COUNT(*) as Cnt, 
    RANK() OVER (
       PARTITION BY CustomerID
       ORDER BY COUNT(*) DESC
    ) AS Rnk 
    FROM YourTransactionTable
    GROUP BY CustomerID, ProdID
) x 
WHERE Rnk = 1

这个使用了 RANK() 函数。在这种情况下，您不必重新加入相同的 table（这意味着需要的工作要少得多）

现在要更新您现有的数据，我喜欢将我的数据集包装在 WITH 中，以使调试更容易一些，最终更新也更简单一些：

;WITH
(
  SELECT CustomerID, ProdID, Cnt 
  FROM 
  (
     SELECT CustomerID, ProdID, COUNT(*) as Cnt, 
     RANK() OVER (PARTITION BY CustomerID
     ORDER BY COUNT(*) DESC) AS Rnk 
     FROM TransactionTable
     GROUP BY CustomerID, ProdID
  ) x 
  WHERE Rnk = 1
) As SRC

 UPDATE FavouriteTable
 SET Favourite = SRC.ProdID
 FROM SRC
 WHERE SRC.CustomerID = Favourite.CustomerID

Answer 5

为了 return 完全按照您在问题中描述的行，您可以尝试使用 table 表达式（我在示例中使用了 CTE）首先 return a人气排名，数字越高，产品越受每位顾客欢迎。

WITH RankTable AS (
  SELECT
    CustomerID, ProductID, COUNT(*) AS Popularity
  FROM TableA
  GROUP BY CustomerID, ProductID
)

然后可以通过首先对原始 table（TableA）和 table 表达式（RankTable）执行内部联接来 return 编辑完整结果 table ，然后使用 window 函数在 FavoriteProduct 列中创建值。

SELECT 
    P.CustomerID
  , P.ProductID
  , FIRST_VALUE(P.ProductID) OVER(
      PARTITION BY R.CustomerID
      ORDER BY R.Popularity DESC, R.ProductID) AS FavoriteProduct
FROM TableA AS P
  INNER JOIN RankTable AS R
    ON P.CustomerID = R.CustomerID
    AND P.ProductID= R.ProductID;

在 sql 服务器 2012 中查找最频繁的值

Finding the most frequent value in sql server 2012

sql

sql-server

pivot

sql-server-2012