HOW TO:SQL Server根据其他字段中的最大值选择不同的字段 [英] HOW TO: SQL Server select distinct field based on max value in other field

问题描述

id   tmpname      date_used        tkt_nr
---|---------|------------------|--------|
1  | template| 04/03/2009 16:10 | 00011  |
2  | templat1| 04/03/2009 16:11 | 00011  |
5  | templat2| 04/03/2009 16:12 | 00011  |
3  | diffname| 03/03/2009 15:11 | 00022  |
4  | diffname| 03/03/2009 16:12 | 00022  |
6  | another | 03/03/2009 16:13 | NULL   |
7  | somethin| 24/12/2008 11:12 | 00023  |
8  | name    | 01/01/2009 12:12 | 00026  |

我想得到结果:

id   tmpname      date_used        tkt_nr
---|---------|------------------|--------|
5  | templat2| 04/03/2009 16:12 | 00011  |
4  | diffname| 03/03/2009 16:12 | 00022  |
7  | somethin| 24/12/2008 11:12 | 00023  |
8  | name    | 01/01/2009 12:12 | 00026  |

所以我要寻找的是基于datetime的最大值具有不同的tkt_nr值(不包括NULL).

So what I'm looking for is to have distinct tkt_nr values excluding NULL, based on the max value of datetime.

我尝试了几种选择，但总是失败

I have tried several options but always failed

SELECT *
FROM  templateFeedback a 
JOIN (
      SELECT ticket_number, MAX(date_used) date_used
      FROM   templateFeedback
      GROUP BY ticket_number
     ) b 
ON a.ticket_number = b.ticket_number AND a.date_used = b.date_used

我将不胜感激.不幸的是，我需要代码与SQL Server兼容.

I would appreciate any help. Unfortunately I need the code to be compatible with SQL Server.

推荐答案

自从我发现窗口函数以来，我就停止了这种方式.经常有两个记录具有相同的时间戳记，而我在结果集中得到两个记录.这是tSQL的代码.与Oracle类似.我认为mySQL还不支持.

I've stopped doing things this way since I discovered windowing functions. Too often, there are two records with the same timestamp and I get two records in the resultset. Here's the code for tSQL. Similar for Oracle. I don't think mySQL supports this yet.

Select id, tmpname, date_used, tkt_nbr
From 
(
    Select id, tmpname, date_used, tkt_nbr,
        rownum = Row_Number() Over (Partition by tkt_nbr Order by date_used desc)
) x
Where row_num=1

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