Mysql 创建sql查询以获取每个单元id的单个最新值

我正在做这个项目，我需要做的一件事就是选择一些数据

表:

id | unit_id | data1 | data2 | data 3 | data4 | TimeStamp

1 | 1 | 1 | 1 | 1 | 2012-10-18 18:17:42

2 | 1 | 2 | 2 | 2 | 2012-10-18 18:18:42

3 | 1 | 3 | 5 | 3 | 2012-10-20 18:19:42 

4 | 1 | 4 | 7 | 4 | 2012-10-21 18:20:42 

5 | 1 | 5 | 8 | 8 | 2012-10-22 18:21:42 

6 | 2 | 1 | 1 | 1 | 2012-10-18 18:17:42 

7 | 2 | 2 | 2 | 4 | 2012-10-19 18:18:42 

8 | 2 | 3 | 2 | 5 | 2012-10-20 18:19:42 

9 | 2 | 4 | 3 | 6 | 2012-10-21 18:20:42 

---

我需要的是，为每个单元id获取单个最新值，下面的查询将按单元id对记录进行分组，并标识具有最新时间戳的记录，将这些结果与相同的表连接，并选择具有单元id和时间戳值的记录

SELECT 
    a.* 
FROM 
    MyTable a
    JOIN (SELECT 
              unit_id, 
              MAX(TimeStamp) 'TimeStamp' 
          FROM 
              MyTable 
          GROUP BY unit_id
         ) as b
    ON a.unit_id = b.unit_id AND a.Timestamp = b.TimeStamp

---

下面的查询将按unit_id对记录进行分组，并标识具有最新时间戳的记录，将这些结果与同一个表联接，并选择具有unit_id和时间戳值的记录

SELECT 
    a.* 
FROM 
    MyTable a
    JOIN (SELECT 
              unit_id, 
              MAX(TimeStamp) 'TimeStamp' 
          FROM 
              MyTable 
          GROUP BY unit_id
         ) as b
    ON a.unit_id = b.unit_id AND a.Timestamp = b.TimeStamp

---

通过使用GROUPBY子句，如

SELECT 
    unit_id, max(TimeStamp)
FROM 
    table3
GROUP BY 
    unit_id

---

通过使用GROUPBY子句，如

SELECT 
    unit_id, max(TimeStamp)
FROM 
    table3
GROUP BY 
    unit_id

试试这个

SELECT unit_id , max(tstamp) 
FROM   t 
GROUP BY unit_id

试试这个

SELECT unit_id , max(tstamp) 
FROM   t 
GROUP BY unit_id