mysql - mySql 查询中的多个时间聚合

Question

我设法按时间聚合一个值，给出如下查询结果：

SELECT date(takenat) AS takendate,
         hour(takenat) AS HourTaken, 
         avg(reading) AS ch1av 
FROM readings 
WHERE channelid = 4 
GROUP BY takendate, HourTaken 
ORDER BY takenat, HourTaken

一些示例输出：

takendate HourTaken ch1av

2013-01-01 0 105.5082
2013-01-01 1 107.2167
2013-01-01 2 106.4833
2013-01-01 3 107.0333

但是，我希望有多个 channelid 的结果（在同一个查询中）

takedate HourTaken ch1av ch2av ch4av

因此，例如 channelid=1,2 和 4 的每小时平均值

我尝试了子查询，但我的 sql foo 还不够！

Answer 1

IN如果您有多个条件，请使用，

select date(takenat) AS takendate,
       hour(takenat) AS HourTaken, 
       avg(reading) AS ch1av,
       channelid 
from   readings 
where  channelid IN (1,2,4)
group  by takendate, HourTaken, channelid 
order  by takenat, HourTaken

这与使用相同OR

select date(takenat) AS takendate,
       hour(takenat) AS HourTaken, 
       avg(reading) AS ch1av,
       channelid  
from   readings 
where  channelid = 1 OR 
       channelid = 2 OR
       channelid = 4
group  by takendate, HourTaken, channelid
order  by takenat, HourTaken

Answer 2

听起来你想要这样的东西：

SELECT DATE(takenat) AS takendate,
       HOUR(takenat) AS HourTaken,
       AVG(CASE WHEN channelid = 1 THEN reading ELSE null END) AS ch1av, 
       AVG(CASE WHEN channelid = 2 THEN reading ELSE null END) AS ch2av, 
       AVG(CASE WHEN channelid = 4 THEN reading ELSE null END) AS ch4av
FROM readings 
WHERE channelid IN (1,2,4)
GROUP BY takendate, HourTaken
ORDER BY takenat, HourTaken