MySQL的左連接的日期與秩序

sensors:

id name key code 
1 s1 abc 123 
2 s2 def 456 
3 s3 ghi 789

measurements:

id value sensor_id generated_at 
1 1.0 1   2013-12-30 06:00:00 
2 1.0 1   2013-12-30 06:01:00 
3 1.0 1   2013-12-30 06:02:00 
4 3.0 2   2013-12-30 07:00:00 
5 3.0 2   2013-12-30 07:01:00 
6 3.0 2   2013-12-30 07:05:00 
7 5.0 3   2013-12-30 08:02:00 
8 5.0 3   2013-12-30 08:03:00 
9 5.0 3   2013-12-30 08:11:00 
10 5.0 3   2013-12-30 08:15:00

我想要做的是產生的所有傳感器的數據報告，包括第一次和最後一次接收測量的時間爲generated_at，所以MySQL請求的結果應該如下所示：

id name key code first_value_generated_at last_value_generated_at 
1 s1 abc 123 2013-12-30 06:00:00  2013-12-30 06:02:00 
2 s2 def 456 2013-12-30 07:00:00  2013-12-30 07:05:00 
3 s3 ghi 789 2013-12-30 08:02:00  2013-12-30 08:15:00

我將不勝感激任何幫助，謝謝。

來源

2014-04-18 Rustam A. Gasanov

我不認爲LEFT JOIN是這裏真的有必要（僅在情況下，當有更多的還是比measurements.sensor_id少sensors.id）。 SQL查詢低於：

SELECT 
    s.id, 
    s.name, 
    s.key, 
    s.code, 
    m.first_value_generated_at, 
    m.last_value_generated_at 
FROM sensors s JOIN 
    (SELECT 
     sensor_id, 
     MIN(generated_at) as first_value_generated_at, 
     MAX(generated_at) as last_value_generated_at 
    FROM 
     measurements 
    GROUP BY 
     sensor_id 
    ) m ON s.id = m.sensor_id 
ORDER BY 
    s.id

來源

2014-04-18 08:01:53 potashin

我得到'您的SQL語法錯誤;檢查與您的MySQL服務器版本相對應的手冊，在'FROM measurements'附近使用正確的語法 –

只需從MAX（m.generated_at）中取出逗號作爲last_value_generated_at，並且查詢應該可以工作 –

@Rustam A. Gasanov：更新了我的帖子。 – potashin

我希望這應該爲你工作，

select * 
    ,(select min(generated_at) from measurements as a where a.sensor_id =s.id) as first_value_generated_at 
    ,(select max(generated_at) from measurements as b where b.sensor_id =s.id) as last_value_generated_at 
from sensors as s

來源

2014-04-18 08:00:12 AK47

這也許能做到這一點 - 嵌套選擇？

 select sensors.id, sensors.name, sensors.key, sensors.code, 
    (select generated_at from measurements order by time asc limit 1) 
as first_value_generated_at, 
    (select generated_at from measurements order by time desc limit 1) 
as last_value_generated_at from sensors

來源

2014-04-18 08:05:58 FanaticD

嘗試此查詢，就會產生精確的輸出，你需要

select s.id,s.name,s.key,s.code,min(m.generated_at) first_vaue_generated_at,max(m.generated_at) last_value_generated_at 
     from sensors s 
LEFT JOIN measurements m ON (s.id = m.sensor_id) 
    group by 1,2,3,4;

來源

2014-04-18 08:17:57 rocks

試試這個它會工作

select s.id,s.name,s.key,s.code,m.generated_at as first_value_generated_at,ml.generated_at as last_value_generated_at from sensors as s,measurements as mf,measurements as ml where s.id = mf.sessor_id and s.id = ml.sensor_id and mf.generated_at < ml.generated_at group by mf.sensor_id

來源

2014-04-18 08:18:23 pravi

MySQL的左連接的日期與秩序

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