选择两个不同列的最新条目

Question

I've been at it for hours trying to figure this out but no luck. I'm trying to get the most recent change to the machine status. Machines have unique names and belong to a few different classes. The following query is the closest I've gotten to what I want, but it doesn't return the latest result. Just distinct Class and Name values.

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

The data table looks like this, but with the rows mixed up.

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

What I'm trying to get is:

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

Many thanks!

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`)