查找每组其他行的最大值

Question

我有一个简单的 table，其中值 (ID) 分组 (GRP_ID)。

create table tst as
select 1 grp_id, 1 id from dual union all
select 1 grp_id, 1 id from dual union all
select 1 grp_id, 2 id from dual union all
select 2 grp_id, 1 id from dual union all
select 2 grp_id, 2 id from dual union all
select 2 grp_id, 2 id from dual union all
select 3 grp_id, 3 id from dual;

使用分析函数很容易找到每组的最大值。

select grp_id, id,
max(id) over (partition by grp_id) max_grp
from tst
order by 1,2;

    GRP_ID         ID    MAX_GRP
---------- ---------- ----------
         1          1          2 
         1          1          2 
         1          2          2 
         2          1          2 
         2          2          2 
         2          2          2 
         3          3          3

但目标是找到不包括当前行值的最大值。

这是预期结果（第 MAX_OTHER_ID 列）：

   GRP_ID         ID    MAX_GRP MAX_OTHER_ID
---------- ---------- ---------- ------------
         1          1          2            2 
         1          1          2            2 
         1          2          2            1 
         2          1          2            2 
         2          2          2            2  
         2          2          2            2 
         3          3          3

请注意，在 GRP_ID = 2 中，MAX 值存在平局，因此 MAX_OTHER_ID 保持不变。

我确实解决了这个两步解决方案，但我想知道是否有更直接、更简单的解决方案。

with max1 as (
select grp_id, id,
row_number() over (partition by grp_id order by id desc) rn
from tst
)
select GRP_ID, ID, 
case when rn = 1 /* MAX row per group */ then
  max(decode(rn,1,to_number(null),id)) over (partition by grp_id)
else
   max(id) over (partition by grp_id)
end as max_other_id   
from max1
order by 1,2

;

Answer 1

我希望 window 函数支持多个范围规范，例如：

max(id) over (
        partition by grp_id 
        order by id 
        range between unbounded preceding and 1 preceding
        or range between 1 following and unbounded following
        )

但不幸的是他们没有。

作为解决方法，您可以避免子查询和 CTE 在不同范围内两次使用该函数，并在其上调用 coalesce。

select grp_id,
    id,
    coalesce(
            max(id) over (
                partition by grp_id
                order by id 
                range between 1 following and unbounded following
                )
            , max(id) over (
                partition by grp_id 
                order by id 
                range between unbounded preceding and 1 preceding
                )
            ) max_grp
from tst
order by 1,
    2

Coalesce 开箱即用，因为排序子句作为 window 函数调用的结果将是给定 window 中的最大值或空值。

演示 - http://rextester.com/SDXVF13962

Answer 2

SELECT GRP_ID,ID, (SELECT Max(ID)  FROM TEST A WHERE A.ROWID<>B.ROWID AND A.GRP_ID=B.GRP_ID) maX_ID FROM TEST B;

通过 Co-Related Query 获得了预期的结果！希望这有帮助。

查找每组其他行的最大值

Find Maximal Value of other Rows per Group

oracle

analytic-functions