Question

我有一张这样的表：

SELECT * FROM orders;

 client_id | order_id | salesman_id | price
-----------+----------+-------------+-------
         1 |      167 |           1 |    65
         1 |      367 |           1 |    27
         2 |      401 |           1 |    29
         2 |      490 |           2 |    48
         3 |      199 |           1 |    68
         3 |      336 |           2 |    22
         3 |      443 |           1 |    84
         3 |      460 |           2 |    92

我想为每个独特的销售人员和客户端对找到每个最高价销售的order_ids数组。在这种情况下，我想要结果表：

 salesman_id |   order_id
-------------+----------------
           1 | {167, 401, 443}
           2 | {490, 460}

到目前为止，我有一个查询大纲：

SELECT salesman_id, max_client_salesman(order_id)
FROM orders
GROUP BY salesman_id;

但是我在编写aggregate function max_client_salesman。

时遇到了麻烦

postgres中聚合函数和数组的联机文档非常少。任何帮助表示赞赏。

Answer 1

标准SQL

我会将window function last_value() or firstvalue()和DISTINCT结合起来，以有效的方式获得每个(salesman_id, client_id)最高价格的订单，然后将其汇总到您要查找的数组中，使用简单的{{ 3}}

SELECT salesman_id
      ,array_agg(max_order_id) AS most_expensive_orders_per_client
FROM  (
   SELECT DISTINCT
          salesman_id, client_id
         ,last_value(order_id) OVER (PARTITION BY salesman_id, client_id
                                     ORDER BY price
                                     ROWS BETWEEN UNBOUNDED PRECEDING
                                     AND UNBOUNDED FOLLOWING) AS max_order_id
   FROM   orders
   ) x
GROUP  BY salesman_id
ORDER  BY salesman_id;

返回：

 salesman_id |  most_expensive_orders_per_client
-------------+------------------------------------
           1 | {167, 401, 443}
           2 | {490, 460}

aggregate function array_agg()

如果每个(salesman_id, client_id)有多个最高价格，则此查询只会选择一个 order_id - 因为缺乏定义。

对于此解决方案，必须了解窗口函数是在DISTINCT之前应用的。如何将DISTINCT与窗口函数结合使用：

SQL Fiddle.

有关ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING的说明，请参阅PostgreSQL: running count of rows for a query 'by minute'。

使用非标准this closely related answer on dba.SE

进行简化

PostgreSQL实现了SQL标准的扩展DISTINCT ON。有了它，您可以根据一组定义的列非常有效地选择唯一的行它不会比这更简单或更快：

SELECT salesman_id
      ,array_agg(order_id) AS most_expensive_orders_per_client
FROM  (
   SELECT DISTINCT ON (1, client_id)
          salesman_id, order_id
   FROM   orders
   ORDER  BY salesman_id, client_id, price DESC
   ) x
GROUP  BY 1
ORDER  BY 1;

DISTINCT ON

我还使用位置参数来缩短语法。详细说明：

SQL Fiddle.

Answer 2

我认为您希望Postgres功能array_agg与row_number()结合使用但是，您对查询的描述对我来说没有意义。

以下内容为销售员提供客户和销售人员以及最高价订单的订单列表：

select client_id, salesman_id, array_agg(order_id)
from (select o.*,
             row_number() over (partition by salesman_id order by price desc) as sseqnum,
             row_number() over (partition by client_id order by price desc) as cseqnum
      from orders o
     ) o
where sseqnum = 1
group by salesman_id, client_id

我不知道“每个销售人员和客户的最高销售额”是什么意思。也许你想要：

where sseqnum = 1 or cseqnum = 1

每个销售人员的最高价格汇总

2 个答案:

标准SQL

使用非标准this closely related answer on dba.SE