Question

我正在计算5个最后一个进程执行的平均值，因为我使用子查询，因为limit子句将计算所有执行的平均值而不仅仅是5.我的问题是在我的子查询中我有一个未知的列错误where子句。我应该使用join而不是子查询吗？我怎样才能做到这一点？

SELECT s.id, s.name,ssch.name,s.refresh_delay,
(SELECT MAX(start_time) FROM runs    WHERE sp_id = s.id) AS    last_run_started,
(SELECT MAX(start_time) FROM runs WHERE sp_id = s.id AND sp_run_status_id = 27  AND confidence_level >= 90 AND manual_approval_id IN (0,1)) AS last_run_accepted,
(SELECT last_run_started + INTERVAL 15 MINUTE) AS dwt,
(SELECT SEC_TO_TIME(AVG(TIME_TO_SEC(times.completion_time) - TIME_TO_SEC(times.start_time))) AS tw FROM 
(SELECT completion_time, start_time FROM runs **WHERE  sp_id = s.id** LIMIT 5) times) tw
  FROM spouses s 
LEFT JOIN `time_zones` tz ON tz.`id` = `time_zone_id`

Answer 1

这是您的查询，简化为仅显示问题的重要部分：

SELECT s.id, s.name, ssch.name, s.refresh_delay,
       (SELECT SEC_TO_TIME(AVG(TIME_TO_SEC(times.completion_time) -TIME_TO_SEC(times.start_time))) AS tw
        FROM (SELECT completion_time, start_time
              FROM runs
              **WHERE  sp_id = s.id**
              LIMIT 5
             ) times
       ) tw
FROM spouses s LEFT JOIN
     `time_zones` tz 
     ON tz.`id` = `time_zone_id`;

这个逻辑有两个问题：

（最重要的）MySQL不支持嵌套子查询中的相关子句。也就是说，correlation子句可以引用外部查询，但不能引用外部外部查询。
其次，使用limit而不使用order by是可疑的。

一种方法是在FROM子句中将聚合作为子查询进行，使用变量枚举每个sp_id的行：

SELECT s.id, s.name, ssch.name, s.refresh_delay,
       t.tw
FROM spouses s LEFT JOIN
     `time_zones` tz 
     ON tz.`id` = `time_zone_id` LEFT JOIN
     (SELECT sp_id, SEC_TO_TIME(AVG(TIME_TO_SEC(times.completion_time) -TIME_TO_SEC(times.start_time))) AS tw
      FROM (SELECT sp_id, completion_time, start_time,
                   (@rn := if(@spid = sp_id, @rn + 1,
                              if(@spid := sp_id, 1, 1)
                             )
                   ) as seqnum
            FROM runs r CROSS JOIN
                 (SELECT @spid := 0, @rn := 0) params
            ORDER BY sp_id, start_time desc
           ) times
      WHERE seqnum <= 5    
      GROUP BY sp_id
     ) t
     ON t.sp_id = s.id

subquery-of-subquery的where子句中的未知列

1 个答案: