SQL 查询：这可以在没有嵌套查询的情况下完成吗？

Question

下面的查询有效，但计算量很大（有 > 14k 条记录）；这可以更有效地完成吗（例如，没有嵌套查询）？基本上，它匹配同一 table 中的实例，这些实例代表一个开启命令 (log1) 和第一个关闭命令 (log2)。

SELECT log1.`deviceID`, log1.`timestamp` AS `on`, log2.`timestamp` as `off` 
FROM `HC2_log_raw` log1, `HC2_log_raw` log2 
WHERE log1.`newValue` > 0 AND log1.`oldValue` = 0 AND log2.`newValue` = 0 AND log1.`deviceID` = log2.`deviceID` AND 
    log2.`timestamp` = 
    (SELECT MIN(log3.`timestamp`) 
    FROM `HC2_log_raw` log3 
    WHERE log3.`timestamp` > log1.`timestamp` AND log3.`deviceID` = log1.`deviceID` AND log3.`newValue`=0)

谢谢！

Answer 1

看看这个。 afaik，where 子句比加入 on 条件更好。

SELECT log1.`deviceID`
    ,log1.`timestamp` AS `on`
    ,log2.`timestamp` AS `off`
FROM 
`HC2_log_raw` log1
inner join `HC2_log_raw` log2
on 
log1.`deviceID` = log2.`deviceID`
where
(
    log1.`newValue` > 0
AND log1.`oldValue` = 0
AND log2.`newValue` = 0
AND log2.`timestamp` = (
        SELECT MIN(log3.`timestamp`)
        FROM `HC2_log_raw` log3
        WHERE log3.`timestamp` > log1.`timestamp`
            AND log3.`deviceID` = log1.`deviceID`
            AND log3.`newValue` = 0
        )
)

Answer 2

您可以尝试使用 JOIN 与 GROUP BY 和 MIN 函数来归档您的预期结果

SELECT log1.`deviceid`, 
       log1.`timestamp`      AS `on`, 
       MIN(log2.`timestamp`) AS `off` 
FROM   `hc2_log_raw` log1 
       INNER JOIN `hc2_log_raw` log2 
               ON log1.`deviceid` = log2.`deviceid` 
                  AND log1.`timestamp` < log2.`timestamp` 
WHERE  log1.`newvalue` > 0 
       AND log1.`oldvalue` = 0 
       AND log2.`newvalue` = 0 
GROUP  BY log1.`deviceid`, log1.`timestamp`

SQL 查询：这可以在没有嵌套查询的情况下完成吗？

SQL query: can this be done without a nested query?

mysql

sql

nested-queries