mysql - 如何将一列拆分为按日期排序的多列

Question

在尝试以正确格式获取数据库数据时，我遇到了很多问题。我正在寻找按天按列打印数据库输出的方法。

我的数据库有两列，一列带有时间戳，格式如YYYY-MM-DD H:M，另一列包含与速度相关的数据。

我需要按天将速度数据拆分成列。

或多或少，我的数据库是这样的(每天有 288 条数据):

 Timestamp          |   Speed

2014-05-01 00:03:00 |   328.71    
2014-05-01 00:18:00 |   331.31    
2014-05-01 00:33:00 |   193.83        
2014-05-02 00:03:00 |   321.21    
2014-05-02 00:18:00 |   290.39    
2014-05-02 00:33:00 |   283.43

我正在寻找的是:

Hour    | 2014-05-01 | 2014-05-02

00:03:00 | 328.71    | 321.21     
00:18:00 | 331.31    | 290.39    
00:33:00 | 193.83    | 283.43

首先，我尝试过以静态的方式进行，但是当我得到它时，我会进行动态的。

我的查询是

SELECT 
(CASE WHEN Timestamp>='2014-05-01' AND Timestamp<='2014-05-03' 
    THEN date_format(Timestamp,'%H:%i') ELSE 0 END) AS 'Hour', 
(CASE WHEN Timestamp>='2014-05-01' AND Timestamp<='2014-05-02' 
    THEN speed ELSE 0 END) AS '2014-05-01', 
(CASE WHEN Timestamp>='2014-05-02' AND Timestamp<='2014-05-03' 
    THEN velocidad ELSE 0 END) AS '2014-05-02' 
FROM `db_speed` 
WHERE Timestamp>='2014-05-01' AND Timestamp<='2014-05-10

通过这个查询，我得到了这样的结构:

Hour     | 2014-05-01 | 2014-05-02

00:03:00 | 328.71     | 0     
00:18:00 | 331.31     | 0    
00:33:00 | 193.83     | 0    
00:03:00 | 0          | 321.21     
00:18:00 | 0          | 290.39
00:33:00 | 0          | 283.43

Answer 1

你很接近，你只是缺少 group by 和聚合函数。

SELECT 
(CASE WHEN Timestamp>='2014-05-01' AND Timestamp<='2014-05-03' 
    THEN date_format(Timestamp,'%H:%i') ELSE 0 END) AS 'Hour', 
MAX((CASE WHEN Timestamp>='2014-05-01' AND Timestamp<='2014-05-02' 
    THEN speed ELSE NULL END)) AS '2014-05-01', 
MAX((CASE WHEN Timestamp>='2014-05-02' AND Timestamp<='2014-05-03' 
    THEN speed ELSE NULL END)) AS '2014-05-02' 
FROM `db_speed` 
WHERE Timestamp>='2014-05-01' AND Timestamp<='2014-05-10'
GROUP BY `Hour`

• 看到它在 sqlfiddle 中实时运行