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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