MySQL

Question

我有两个 MySQL 查询要合并。

SELECT DEVICE as Room, VALUE as Temperature FROM `current` WHERE `READING` LIKE 'temperature'
SELECT DEVICE as Room, VALUE as Humidity    FROM `current` WHERE `READING` LIKE 'humidity'

我的数据 Table 如下所示：

DEVICE	VALUE	READING
Arbeitszimmer	52	humidity
Arbeitszimmer	22	temperature
Aussen	88	humidity
Aussen	1.8	temperature

期望的结果应该是：

Room	Temperature	Humidity
Arbeitszimmer	22	52
Aussen	1.8	88

我正在为 SQL 查询而苦恼。

Answer 1

简单的自连接应该可以工作

SELECT c1.DEVICE as Room, c1.VALUE as Temperature, c2.VALUE as Humidity  
FROM `current` c1 
    join `current` c2 on c1.device = c2.device 
        and c1.`READING` = 'temperature'
        and c2.`READING` = 'humidity'

顺便说一句，没有必要使用 like

Answer 2

如果您只有两类值，您将使用具有相同值的联接 table

select a.device, a.value temp, b.value humidity
from current a  
inner join current a.device = b.device 
    and a.reading = 'temperature'
        and b.reading = 'humidity'

Answer 3

一些条件聚合来调整阅读指标。

SELECT `DEVICE` as Room
, MAX(CASE WHEN `READING` = 'temperature' THEN `VALUE` END) as Temperature
, MAX(CASE WHEN `READING` = 'humidity' THEN `VALUE` END) as Humidity
FROM `current` 
WHERE `READING` IN ('temperature', 'humidity') 
GROUP BY `DEVICE`
ORDER BY `DEVICE`

MySQL - 合并具有不同 where 语句的行

MySQL - Combine rows with different where statements

sql

join