如何选择“最大"从表排? [英] How can I select the "maximum" row from a table?

问题描述

如何从表中选择最大的行?最大值是什么意思-我的表有两个时间戳列，TIME1和TIME2.最大列是具有TIME1的最新值的列.如果那不是唯一的行，则最大值为那些行中具有TIME2最新值的那一行.

How can I select the maximum row from a table? What does maximum mean -- well my table has two timestamp columns, TIME1 and TIME2. The maximum column is the one with the latest value for TIME1. If that is not a unique row, then the maximum is the one within those rows with the latest value for TIME2.

如果重要的话，这是在Oracle上的.

This is on Oracle if that matters.

推荐答案

您需要的是"Top-N"查询:

What you need is a "Top-N" query:

从( 从表中选择* 按time1 desc，time2 desc排序 )，其中rownum< 2;

select * from ( select * from table order by time1 desc, time2 desc ) where rownum < 2;

如果您在time1和time2上正确建立索引，那将非常快:

if you properly index on time1, time2 it will be very fast:

http://blog.fatalmind.com/2010/07/30/analytic-top-n-queries/

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