sql - 使用 PostgreSQL 区分计数

Question

我正在尝试更改下面查询的计数 DISTINCT 部分，因为当前查询返回的 WINDOW 定义不受支持。使用 PostgreSQL 进行此计算的最无缝方法是什么？谢谢。

SELECT transaction_date, brand, Description, Amount, newval
into temp.table
FROM (SELECT transaction_date, brand, Description, Amount,
         (Amount / count(DISTINCT unique_mem_id) over (partition by to_char(transaction_date, 'YYYY-MM'),brand
         )) as newval
  FROM source.table
 )
WHERE DESCRIPTION iLIKE '%Criteria%';

Answer 1

由于用例，拆分代码似乎更好。

根据以下查询创建表month_brand:

select      to_char(transaction_date, 'YYYY-MM')    as yyyymm
           ,brand
           ,count (distinct unique_mem_id)          as count_distinct_unique_mem_id

from        source.table

group by    yyyymm
           ,brand
;

将 month_brand 加入您的源表:

select      t.transaction_date, t.brand, t.Description, t.Amount, t.Amount / m.count_distinct_unique_mem_id as newval

from                    source.table    as t

            join        month_brand     as m

            on          m.yyyymm = to_char(t.transaction_date, 'YYYY-MM')    

where       t.description ilike '%Criteria%'
;

---

代替 count(distinct ...)，两阶段解决方案:

1. 为重复的 unique_mem_id 提供行号
2. 只计算 row_number = 1 的 unique_mem_id

---

select  *

into     temp.table

from   (SELECT  transaction_date, brand, Description, Amount, 
                (Amount / count(case rn when 1 then unique_mem_id end) over (partition by to_char(transaction_date, 'YYYY-MM'),brand)) as newval

        FROM    (SELECT     transaction_date, brand, Description, Amount,unique_mem_id
                            row_numner () over (partition by to_char(transaction_date, 'YYYY-MM'),brand,unique_mem_id) as rn

                 FROM       source.table
                 )
        )

WHERE   DESCRIPTION iLIKE '%Criteria%'
;