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        GROUP BY 与 MAX(DATE)

        GROUP BY with MAX(DATE)(GROUP BY 与 MAX(DATE))

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                1. 本文介绍了GROUP BY 与 MAX(DATE)的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着跟版网的小编来一起学习吧!

                  问题描述

                  我正在尝试在表格中列出每列火车的最新目的地(最大出发时间),forz/a>:

                  I'm trying to list the latest destination (MAX departure time) for each train in a table, for example:

                  Train    Dest      Time
                  1        HK        10:00
                  1        SH        12:00
                  1        SZ        14:00
                  2        HK        13:00
                  2        SH        09:00
                  2        SZ        07:00
                  

                  想要的结果应该是:

                  Train    Dest      Time
                  1        SZ        14:00
                  2        HK        13:00
                  

                  我试过使用

                  SELECT Train, Dest, MAX(Time)
                  FROM TrainTable
                  GROUP BY Train
                  

                  我收到了ora-00979 not a GROUP BY expression"错误,提示我必须在 group by 语句中包含Dest".但这肯定不是我想要的......

                  by I got a "ora-00979 not a GROUP BY expression" error saying that I must include 'Dest' in my group by statement. But surely that's not what I want...

                  是否可以在一行 SQL 中完成?

                  Is it possible to do it in one line of SQL?

                  推荐答案

                  您不能在结果集中包含未分组的非聚合列.如果一列火车只有一个目的地,那么只需将目的地列添加到您的 group by 子句中,否则您需要重新考虑您的查询.

                  You cannot include non-aggregated columns in your result set which are not grouped. If a train has only one destination, then just add the destination column to your group by clause, otherwise you need to rethink your query.

                  试试:

                  SELECT t.Train, t.Dest, r.MaxTime
                  FROM (
                        SELECT Train, MAX(Time) as MaxTime
                        FROM TrainTable
                        GROUP BY Train
                  ) r
                  INNER JOIN TrainTable t
                  ON t.Train = r.Train AND t.Time = r.MaxTime
                  

                  这篇关于GROUP BY 与 MAX(DATE)的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持跟版网!

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