查询运行太慢甚至停止，因为超过 17000 行的时间

Question

我有 table 1:

historial_id	timestamp	address	value	insertion_time
1	2022-01-29	1	84	2022-01-31
2	2022-01-29	2	40	2022-01-31
3	2022-01-30	1	84	2022-01-31
4	2022-01-30	2	41	2022-01-31
5	2022-01-30	2	41	2022-01-31

（有时会重复行）

...

我需要一个查询来获取：

timestamp	value(address 1)	value(address 2)
2022-01-29	84	40
2022-01-30	84	41

......

我试过：

SELECT timestamp, ( SELECT value 
                   FROM historical 
                   WHERE register_type=11 
                   AND address=2
                   AND timestamp=t1.timestamp
                   GROUP BY value 
                   ) AS CORRIENTE_mA,
                ( SELECT value 
                  FROM historical 
                  WHERE register_type=11 
                  AND address=1 
                  AND timestamp=t1.timestamp 
                  GROUP BY value ) AS Q_M3pH
FROM historical AS t1 
GROUP BY timestamp;

但是太慢了，甚至因为超时而停止

我也试过 distinct 而不是 group by

Answer 1

我认为你需要 dynamic pivot。请尽量避免像 timestamp.

这样的 MySQL reserved words

下面查询 return 只有地址 1 和 2 按时间戳分组的最大值。

这是您查询的简化版本：

select
     `timestamp`
   , max(case when address=1 then value  end) as value_address1
   , max(case when address=2 then value  end) as value_address2

from historical
group by `timestamp`;

Result:

  timestamp   value_address1  value_address2
  2022-01-29       84            40
  2022-01-30       84            41

Demo

查询运行太慢甚至停止，因为超过 17000 行的时间

Query runs too slow and even it stops because exceded of time with 17000 rows

mysql

group-by

mariadb

distinct