Question

我有一个更新的条目日志，其中每个票号都有不同类别的更新。例如

|Ticket Number | DateTime    | Update           | Category | 
| I0001        | 2015-07-28  | Spoke to someone | Update   |
| I0002        | 2015-07-28  | Issue started    | Update   | 
| I0002        | 2015-07-27  | Owner changed    | System   | 
| I0002        | 2015-07-26  | Auto Alarm       | System   | 
| I0001        | 2015-07-28  | More affected    | Update   | 
| I0001        | 2015-07-25  | Auto Alarm       | System   |
| I0003        | 2015-07-01  | Assigneed        | Update   |

我希望它有一个列表，显示最后一个DateTime，每个票号和类别的更新，所以我最终会得到类似的东西。

|Ticket Number | DateTime    | Update           | Category | 
| I0001        | 2015-07-28  | Spoke to someone | Update   |
| I0002        | 2015-07-28  | Issue started    | Update   | 
| I0002        | 2015-07-27  | Owner changed    | System   | 
| I0001        | 2015-07-25  | Auto Alarm       | System   |
| I0003        | 2015-07-01  | Assigneed        | Update   |

我已经尝试了一些方法，但还没有接近完成它。

Answer 1

<强>查询

select t2.`Ticket Number`,
t2.`DateTime`,
t2.`Update`,
t2.Category
from
(
   select t.*, 
   @rownum := @rownum + 1 AS rn
   from tableName t, 
   (select @rownum := 0) r
   order by t.`Ticket Number`,`DateTime` desc
)t2
group by t2.`Ticket Number`,Category
having min(t2.rn)
order by t2.`DateTime` desc,t2.`Ticket Number`;

Fiddle demo

Answer 2

  [WebInvoke(Method = "POST")]

这将为您提供每个故障单和类别的最新信息，如果您还包含[WebInvoke(Method = "POST",BodyStyle=WebMessageBodyStyle.WrappedRequest)]字段，您将获得由于该组而获得的每张故障单的大量记录。

如果您想要一个与您发布的结果集匹配的查询，则必须使用子选择或排名功能来执行此操作。

select `Tickte number`, max(`datetime`), category from `table`

这未经过测试，但应该能满足您的需求。

Mysql获取group by的最新条目

2 个答案: