在MySQL表中进行透视

Question

我有一个名为开关的MySQL表如下：

switchName  switchCondition switchingTime 
----------- --------------- ------------- 
First       ON              10:00      
First       OFF             11:00
Second      ON              10:30      
Third       OFF             13:00      
Third       ON              13:45  

如何通过根据切换条件调整切换时间，使用上表以下列格式显示报告为html表？

switchName   ON     OFF 
----------- -----  -------
First       10:00   11:00                   
Second      10:30    -        
Third       13:45   13:00

Answer 1

试试这个：

SELECT s.switchName, 
       MAX(CASE WHEN s.switchCondition = 'ON' THEN s.switchingTime ELSE '-' END) AS SwitchON, 
       MAX(CASE WHEN s.switchCondition = 'OFF' THEN s.switchingTime ELSE '-' END) AS SwitchOFF
FROM switches s 
GROUP BY s.switchName;

Answer 2

另一种方法

SELECT s.switchName, s1.switchingTime, s2.switchingTime
FROM switches s
LEFT JOIN switches s1 ON s.switchName = s1.switchName AND s1.switchCondition = 'ON'
LEFT JOIN switches s2 ON s.switchName = s2.switchName AND s2.switchCondition = 'OFF'
GROUP BY s.switchName

（虽然它代表您的短划线NULL）