根据由另一列分组的不同列的最大值获取值

问题描述

我想根据由另一列分组的不同列的最大值来获取列的值.

I want to get the values of a column based on max of a different column grouped by another column.

我有这张桌子:

KEY NUM VAL
A   1   AB
B   1   CD
B   2   EF
C   2   GH
C   3   HI
D   1   JK
D   3   LM

想要这个结果:

KEY VAL
A   AB
B   EF
C   HI
D   LM

我实际上可以使用这个查询来获取它.

I could actually use this query to get it.

select KEY, VAL
from TABLE_NAME TN
where NUM = (
    select max(NUM)
    from TABLE_NAME TMP
    where TMP.KEY = TN.KEY
    )

但是在 ORACLE SQL(10g 或以上)中有更优雅的方式来获得结果吗?

However is there a more elegant way in ORACLE SQL (10g or above) to get the result?

背后的原因是实际上有多个KEY，只是看起来有点难看.

Reason behind it is that there are actually multiple KEYs and it just looks a bit ugly.

推荐答案

您可以使用 row_number() 来解决这个问题:

You can approach this using row_number():

select key, val
from (select t.*, row_number() over (partition by key order by num desc) as seqnum
      from table_name t
     ) t
where seqnum = 1;

你是否认为这更优雅"可能是一个品味问题.

Whether you consider this more "elegant" is probably a matter of taste.

我应该指出，这与您的查询略有不同.这保证为每个 key 返回一行；你的可以返回多行.如果您想要这种行为，只需使用 rank() 或 dense_rank() 而不是 row_number().

I should point out that this is subtly different from your query. This is guaranteed to return one row for each key; yours could return multiple rows. If you want that behavior, just use rank() or dense_rank() instead of row_number().

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