Question

我已经花了几个小时试图解决这个问题，但没有运气。我试图获取机器状态的最新更改。机器具有唯一的名称，属于几个不同的类。以下查询是我最接近我想要的，但它没有返回最新结果。只是不同的类和名称值。

SELECT * FROM ( SELECT * FROM MachineStatus ORDER BY date DESC ) AS ord GROUP BY class, name

数据表看起来像这样，但行混合了。

Class     Name     Status     Date
 A        NXP      ONLINE     2015-02-17
 A        NXP      OFFLINE    2015-02-10
 A        AVR      STANDBY    2015-02-16
 A        AVR      OFFLINE    2015-01-05
 A        PIC      ONLINE     2015-02-01
 A        PIC      STANDBY    2015-01-05

 B        TXI      ONLINE     2015-02-10
 B        TXI      STANDBY    2015-02-07
 B        FSC      ONLINE     2015-02-17
 B        FSC      OFFLINE    2015-02-01

 C        STM      OFFLINE    2015-02-17
 C        STM      STANDBY    2015-02-10
 C        INT      ONLINE     2015-01-01
 C        INT      STANDBY    2014-11-10

我想要得到的是：

 A        NXP      ONLINE     2015-02-17
 A        AVR      STANDBY    2015-02-16
 A        PIC      ONLINE     2015-02-01
 B        TXI      ONLINE     2015-02-10
 B        FSC      ONLINE     2015-02-17
 C        STM      OFFLINE    2015-02-17
 C        INT      ONLINE     2015-01-01

非常感谢！

Answer 1

SELECT t.Class, t.Name, t.Status, t.Date
FROM my_table t
  INNER JOIN (SELECT Class, Name, MAX(Date) AS Date
    FROM my_table
    GROUP BY Class, Name
  ) sub ON (sub.Class = t.Class AND sub.Name = t.Name AND sub.Date = t.Date)
GROUP BY t.Class, t.Name

Answer 2

应该像......一样直截了当。

SELECT `table`.* FROM `table` GROUP BY `name` HAVING `date` = MAX(`date`)

选择两个不同列的最新条目

2 个答案: