sql - 获取 Oracle 上每个值的第二大最大值

Question

我想使用 PL/SQL (Oracle) 获得第二高的最大值。

我有一个如下所示的表格:

CLIENT | ORDER_DATE
1      | 14/09/2018
1      | 01/02/2019
2      | 13/12/2019
2      | 01/01/2020
2      | 15/12/2019

我想获得一个表，其中包含每个客户的最大值(ORDER_DATE)和第二高的最大值(ORDER_DATE):

CLIENT | MAX(ORDER_DATE) | 2nd highest max(ORDER_DATE)
1      | 01/02/2019      | 14/09/2018
2      | 01/01/2020      | 15/12/2019

我尝试过使用排名，但只得到一行(一个随机客户端):

select *
  from (select CLIENT,
               max(ORDER_DATE),
               row_number() over (order by max(ORDER_DATE) desc) as rk
          from order_table
         group by CLIENT) t
 where rk = 2

Answer 1

在应用诸如ROW_NUMBER()之类的分析函数后，您需要条件聚合:

WITH t2 AS
(
  SELECT client,order_date,
         ROW_NUMBER() OVER (PARTITION BY client ORDER BY order_date DESC) as rk
   FROM order_table
)
SELECT client, 
       MAX(CASE WHEN rk=1 THEN order_date END) AS "max order date",
       MAX(CASE WHEN rk=2 THEN order_date END) AS "2nd highest max ord.date"
  FROM t2
 GROUP BY client

Demo