根据排名将行转换为列

Posted 2023-03-25

【中文标题】根据排名将行转换为列

【英文标题】：Converting rows into columns based on rank

【发布时间】：2020-05-08 13:04:07

【问题描述】：

我正在尝试根据客户的购买日期（排名）将行转换为列。目标是找到客户购买的第一个、第二个、第三个、第四个和第五个产品类别。我也想知道客户购买了什么产品。

销售表

purchaseDate | productCategory | product      | customer_id | customer_phonenumber | customer_email
2020-05-05     Electronics       iPhone         A001          1234567890             [e-mail]
2020-05-06     Clothing          T-shirt        A001          1234567890             [e-mail]
2020-05-07     Electronics       Keyboard       A001          1234567890             [e-mail]
2020-05-08     Accessories       iPhone Case    A001          1234567890             [e-mail]

结果

customer_id | customer_phoneNumber | customer_email | first_product_category | second_product_category | third_product_category | fourth_product_category | fifth_product_category  | first_product | second_product | third_product | fourth_product | fifth_product
A001          1234567890             [e-mail]     Electonics               Clothing                    Electronics            Accessories               NULL                      iPhone          T-shirt          Keyboard        iPhone Case      NULL

我想知道是否有任何其他方法可以做到这一点，因为我当前的查询花费了太长时间。

这是我的查询：

with ranked_order as (
    select 
        purchaseDate
        , productCategory
        , product
        , customer_id
        , customer_phonenumber
        , customer_email
        , row_number() over(partition by productCategory order by purchaseDate desc) rank
    from sales_table
    )

    select
        customer_id
        , customer_phonenumber
        , customer_email
        , max(case when rank = 1 then productCategory end) first_product_category
        , max(case when rank = 2 then productCategory end) second_product_category
        , max(case when rank = 3 then productCategory end) third_product_category
        , max(case when rank = 4 then productCategory end) fourth_product_category
        , max(case when rank = 5 then productCategory end) fifth_product_category
        , max(case when rank = 1 then product end) first_product
        , max(case when rank = 2 then product end) second_product
        , max(case when rank = 3 then product end) third_product
        , max(case when rank = 4 then product end) fourth_product
        , max(case when rank = 5 then product end) fifth_product
    from 
        ranked_order
    group by 1,2,3

【问题讨论】：

我对你试图通过这个实现的东西感到困惑——我认为将这 10 列添加到每条购买记录中没有什么用处。你能提供一些样本数据和期望的结果吗？如果同一客户在同一天购买了多种产品会怎样？

嗨@GordonLinoff 我刚刚编辑了我的问题。希望它能提供更好的背景和清晰度。我刚刚意识到我在上一个问题中犯了一个错误。

【参考方案1】：

以下是 BigQuery 标准 SQL

#standardSQL
SELECT 
  customer_id, 
  customer_phonenumber, 
  customer_email,
  top5[SAFE_OFFSET(0)].productCategory AS first_product_category,
  top5[SAFE_OFFSET(1)].productCategory AS second_product_category,
  top5[SAFE_OFFSET(2)].productCategory AS third_product_category,
  top5[SAFE_OFFSET(3)].productCategory AS fourth_product_category,
  top5[SAFE_OFFSET(4)].productCategory AS fifth_product_category,
  top5[SAFE_OFFSET(0)].product AS first_product,
  top5[SAFE_OFFSET(1)].product AS second_product,
  top5[SAFE_OFFSET(2)].product AS third_product,
  top5[SAFE_OFFSET(3)].product AS fourth_product,
  top5[SAFE_OFFSET(4)].product AS fifth_product
FROM (
  SELECT customer_id, customer_phonenumber, customer_email,
    ARRAY_AGG(STRUCT(productCategory, product) ORDER BY purchaseDate LIMIT 5) AS top5
  FROM `project.dataset.sales_table`
  GROUP BY customer_id, customer_phonenumber, customer_email
)

【参考方案2】：

我会将值放入数组中：

select customer_id, customer_phonenumber, customer_email,
       array_agg(productCategory order by purchaseDate limit 5) as productCategorys_5,
       array_agg(product order by purchaseDate limit 5) as products_5
from sales_table
group by 1,2,3

这会将值放入数组而不是列中。如果这具有足够好的性能，您可以只索引数组以获取单个元素（尽管我可能会发现数组更方便）。