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我一直在玩这个查询好几天，

select slno,Power_Factor_L32_Avg 
from power_logger pl 
where (pl.slno between 1851219 and 2042099) 
  and meter_id="logger1" 
  and pl.Power_Factor_L32_Avg is not null
  and case when (((pl.slno=1851219) 
                and ((pl.Power_Factor_L32_Avg) not between 0.400 and 1.000)) 
             or ((pl.slno=2042099) and 
                 ((pl.Power_Factor_L32_Avg) not between 0.400 and 1.000)) 
             or ((pl.Power_Factor_L32_Avg not between 0.400 and 1.000) and 
               (((select p2.Power_Factor_L32_Avg 
                  from power_logger p2 
                  where p2.slno=(select slno 
                                 from power_logger 
                                 where slno>pl.slno 
                                   and Power_Factor_L32_Avg is not null 
                                 order by slno asc limit 1)) 
                 between 0.400 and 1.000) 
             or ((select p4.Power_Factor_L32_Avg 
                  from power_logger p4 
                  where p4.slno=(select slno  
                                 from power_logger 
                                 where slno<pl.slno 
                                   and Power_Factor_L32_Avg is not null 
                                 order by slno desc limit 1 )) 
                between 0.400 and 1.000)))) 
           then (case when (((pl.slno=1851219) 
                        and ((select p10.Power_Factor_L32_Avg 
                              from power_logger p10 
                              where p10.slno=pl.slno+1) is null 
                          or (select p10.Power_Factor_L32_Avg 
                              from power_logger p10 
                              where p10.slno=pl.slno+1) between 0.400 and 1.000)) 
                        or (((select p5.Power_Factor_L32_Avg
                              from power_logger p5 
                              where p5.slno=(select slno
                                             from power_logger  
                                              where slno<pl.slno 
                                                and Power_Factor_L32_Avg is not null 
                                              order by slno desc limit 1 )) 
                              between 0.400 and 1.000) 
                          and ((select p6.Power_Factor_L32_Avg 
                                from power_logger p6 
                                where p6.slno=(select slno 
                                               from power_logger 
                                               where slno>pl.slno 
                                                 and Power_Factor_L32_Avg is not null 
                                               order by slno asc limit 1 )) 
                              between 0.400 and 1.000))) 
                      then 0=1 
                      else 1 
                      end) 
             else 0=1 
           end 
order by slno asc

乍一看很难理解查询，但它正在查询具有数百万条记录的表。这里唯一的问题是嵌套查询“ select slno from power_logger where slno<pl.slno and Power_Factor_L32_Avg is not null order by slno desc limit 1”和“ select slno from power_logger where slno>pl.slno and Power_Factor_L32_Avg is not null order by slno desc limit 1”，它们用于查找当前记录的前一个和下一个记录的序列号（slno），分别具有非空值。当这些查询自行运行时，它会在几微秒内给出序列号，但是当包含在上面的查询中时，它会搞砸整个事情，需要明确终止该进程。如果不使用嵌套查询，则上面的查询将在不到 1.5 秒内执行，而是被下一个/上一个序列号替换，无论它是否为空。

这不会去任何地方。感谢是否有人可以帮助我。

使用临时表的新查询，

create temporary table temp(
  id int auto_increment
  ,slno int
  ,pf decimal(10,4)
  ,primary key(id)
);

insert into temp(slno,pf)
(select slno,Power_Factor_L32_Avg 
 from power_logger 
 where slno between 1851219 and 2042099 
 and meter_id='logger1' 
 and Power_Factor_L32_Avg is not null);

select pl.slno,pl.Power_Factor_L32_Avg,t1.slno,t1.pf 
from power_logger pl 
left join temp t1 on t1.slno>pl.slno 
where pl.slno between 1851219 and 2042099 and pl.meter_id='logger1' 
and pl.Power_Factor_L32_Avg is not null;

这是为了测试是否与从 power_logger 表slno一起获取功率因数为空的下一个。slno这也不起作用。我不确定是否有任何其他工作可以在slno不使用大于号的情况下获得下一个。

4

2 回答 2

0

我的观点是，您在案例陈述方面做了太多工作。你也在重复很多工作。

首先，为 p1 中的每一行预先计算 this 的结果，并将其存储在临时表中：

select slno  
from power_logger 
where slno<pl.slno 
  and Power_Factor_L32_Avg is not null 
order by slno desc limit 1

这样做

create temporary table temp(
  slno int
  ,other_slno int
);

INSERT INTO temp(slno, other_slno)(
SELECT main.slno, second.slno
FROM power_logger main 
JOIN (SELECT other.slno FROM power_logger AS other
      where other.slno< main.slno 
      and Power_Factor_L32_Avg is not null 
      order by other.slno desc limit 1) second

);

然后在您的主查询中，执行 SELECT _ FROM power_logger LEFT JOIN temp ON power_logger.slno = temp.slno LEFT JOIN power_logger other ON temp.other_slno = other.slno

这意味着您目前在任何地方都使用类似的东西

 (select p4.Power_Factor_L32_Avg 
              from power_logger p4 
              where p4.slno=(select slno  
                             from power_logger 
                             where slno<pl.slno 
                               and Power_Factor_L32_Avg is not null 
                             order by slno desc limit 1 )

您可以改为将此值作为òther.Power_Factor_L32_Avg.

这将使您每次使用它时访问速度更快。临时表的信息很容易在谷歌上找到，例如。http://www.mysqltutorial.org/mysql-temporary-table/

其次，仅将 CASE 语句用于更简单的条件。您当前的查询在一些 WHEN 语句中具有布尔逻辑，这些语句在相应的 THEN 语句中复制。CASE 的结果是真还是假也是一个不好的迹象。

相反，将布尔逻辑放在 WHERE 中。我已经从您的原始查询中复制并粘贴了以下内容，所以它应该是正确的。

WHERE <Other clauses> ....
  AND (
    ((pl.slno=1851219) 
            and ((pl.Power_Factor_L32_Avg) not between 0.400 and 1.000)) 
         or ((pl.slno=2042099) and 
             ((pl.Power_Factor_L32_Avg) not between 0.400 and 1.000)) 
         or ((pl.Power_Factor_L32_Avg not between 0.400 and 1.000) and 
           (((select p2.Power_Factor_L32_Avg 
              from power_logger p2 
              where p2.slno=(select slno 
                             from power_logger 
                             where slno>pl.slno 
                               and Power_Factor_L32_Avg is not null 
                             order by slno asc limit 1)) 
             between 0.400 and 1.000) 
         or ((select p4.Power_Factor_L32_Avg 
              from power_logger p4 
              where p4.slno=(select slno  
                             from power_logger 
                             where slno<pl.slno 
                               and Power_Factor_L32_Avg is not null 
                             order by slno desc limit 1 )) 
            between 0.400 and 1.000)))

    AND NOT 
        ((pl.slno=1851219) 
            and ((select p10.Power_Factor_L32_Avg 
                  from power_logger p10 
                  where p10.slno=pl.slno+1) is null 
              or (select p10.Power_Factor_L32_Avg 
                  from power_logger p10 
                  where p10.slno=pl.slno+1) between 0.400 and 1.000)) 
              or (((select p5.Power_Factor_L32_Avg
                 from power_logger p5 
                  where p5.slno=(select slno
                                 from power_logger  
                                  where slno<pl.slno 
                                    and Power_Factor_L32_Avg is not null 
                                  order by slno desc limit 1 )) 
                  between 0.400 and 1.000) 
              and ((select p6.Power_Factor_L32_Avg 
                    from power_logger p6 
                    where p6.slno=(select slno 
                                   from power_logger 
                                   where slno>pl.slno 
                                     and Power_Factor_L32_Avg is not null 
                                   order by slno asc limit 1 )) 
                  between 0.400 and 1.000))
  )

这应该有助于缩短时间（特别是使用临时表）。如果没有，则将新版本发布回 SO，我们可以尝试用 'JOIN' 替换一些子查询（这将再次更有效率）。

于 2013-09-27T08:03:02.473 回答
0

通过对 Hbcdev 的答案进行一些修改，

select c.slno,c.Power_Factor_L32_Avg from (select p.slno as cur,a.slno as next,@s1 as prev,(@s1:=p.slno) from (select @s1:=0) d,power_logger p join (SELECT a.slno, @s AS prev, ( @s := a.slno ) ne from power_logger a,(SELECT @s:=0) c where a.slno between 1851219 and 2042099 and a.Power_Factor_L32_Avg is not null and a.meter_id='logger1') as a on a.prev=p.slno where p.slno between 1851219 and 2042099 and p.Power_Factor_L32_Avg is not null and p.meter_id='logger1')d ,power_logger c where c.slno=d.cur and (((c.slno=1851219 or c.slno=2042099) and (c.Power_Factor_L32_Avg not between 0.400 and 1.000)) or ((c.Power_Factor_L32_Avg not between 0.400 and 1.000) and (((select p2.Power_Factor_L32_Avg from power_logger p2 where p2.slno=d.next) between 0.4 and 1.000) or ((select p3.Power_Factor_L32_Avg from power_logger p3 where p3.slno=d.prev) between 0.4 and 1.000)))) and not (((c.slno=1851219) and ((select p10.Power_Factor_L32_Avg from power_logger p10 where p10.slno=c.slno+1) is null or (select p10.Power_Factor_L32_Avg from power_logger p10 where p10.slno=c.slno+1) between 0.400 and 1.000)) or (((select p5.Power_Factor_L32_Avg from power_logger p5 where p5.slno=d.prev) between 0.400 and 1.000) and ((select p6.Power_Factor_L32_Avg from power_logger p6 where p6.slno=d.next) between 0.400 and 1.000))) order by slno asc

这将在大约 6 秒内执行。

于 2013-10-10T02:21:23.813 回答