Question

我有两个数据库表（省略了更多的表）：

acquisitions (acq)
    id {PK}
    id_cu {FK}
    datetime
    { Unique Constraint: id_cu - datetime }

data
    id {PK}
    id_acq {FK acquisitions}
    id_meas
    id_elab
    value

每个可能的id和datetime 全部已编入索引。

当然，我将不更改数据库结构我需要以这种方式提取数据：

按日期时间分组的行
所选data.value组合的每列对应acq.id_cu - data.id_meas - data.id_elab。（见帖子底部的注释）
如果某些列的数据缺失但在日期时间存在其他列

我当前的查询以这种方式构建（请参阅SO question）：

SELECT datetime, MAX(v1) AS v1, MAX(v2) AS v2, MAX(v3) AS v3 FROM (

SELECT acq.datetime AS datetime, data.value AS v1, NULL AS v2, NULL AS v3 
FROM acq INNER JOIN data ON acq.id = data.id_acq
WHERE acq.id_cu = 3 AND data.id_meas = 2 AND data.id_elab = 1

UNION

SELECT acq.datetime AS datetime, NULL AS v1, data.value AS v2, NULL AS v3 
FROM acq INNER JOIN data ON acq.id = data.id_acq
WHERE acq.id_cu = 5 AND data.id_meas = 4 AND data.id_elab = 6

UNION

SELECT acq.datetime AS datetime, NULL AS v1, NULL AS v2, data.value AS v3 
FROM acq INNER JOIN data ON acq.id = data.id_acq
WHERE acq.id_cu = 7 AND data.id_meas = 9 AND data.id_elab = 8

) AS T
WHERE datetime >= "2011-03-01 00:00:00" AND datetime <= "2011-04-30 23:59:59"
GROUP BY datetime

这里仅检索3列，但正如我所说，列通常超过50列。

它完美无缺，但我想知道它是否可以在速度上进行优化。

对于上面的查询，这是MySQL EXPLAIN EXTENDED：

+----+--------------+--------------+------+------------------------------------------------+-----------------------+---------+------------------------+-------+----------+----------------------------------------------+
| id | select_type  | table        | type | possible_keys                                  | key                   | key_len | ref                    | rows  | filtered | Extra                                        |
+----+--------------+--------------+------+------------------------------------------------+-----------------------+---------+------------------------+-------+----------+----------------------------------------------+
|  1 | PRIMARY      | <derived2>   | ALL  | NULL                                           | NULL                  | NULL    | NULL                   | 82466 |   100.00 | Using where; Using temporary; Using filesort |
|  2 | DERIVED      | acquisitions | ref  | PRIMARY,id_cu,ix_acquisitions_id_cu            | id_cu                 | 4       |                        | 18011 |   100.00 |                                              |
|  2 | DERIVED      | data         | ref  | ix_data_id_meas,ix_data_id_acq,ix_data_id_elab | ix_data_id_acq        | 4       | sensor.acquisitions.id |     9 |   100.00 | Using where                                  |
|  3 | UNION        | acquisitions | ref  | PRIMARY,id_cu,ix_acquisitions_id_cu            | ix_acquisitions_id_cu | 4       |                        | 20864 |   100.00 |                                              |
|  3 | UNION        | data         | ref  | ix_data_id_meas,ix_data_id_acq,ix_data_id_elab | ix_data_id_acq        | 4       | sensor.acquisitions.id |     9 |   100.00 | Using where                                  |
|  4 | UNION        | acquisitions | ref  | PRIMARY,id_cu,ix_acquisitions_id_cu            | id_cu                 | 4       |                        | 31848 |   100.00 |                                              |
|  4 | UNION        | data         | ref  | ix_data_id_meas,ix_data_id_acq,ix_data_id_elab | ix_data_id_acq        | 4       | sensor.acquisitions.id |     9 |   100.00 | Using where                                  |
| NULL | UNION RESULT | <union2,3,4> | ALL  | NULL                                           | NULL                  | NULL    | NULL                   |  NULL |     NULL |                                              |
+----+--------------+--------------+------+------------------------------------------------+-----------------------+---------+------------------------+-------+----------+----------------------------------------------+
8 rows in set, 1 warning (8.24 sec)

目前有（编辑：今天检查）390k采集和9.2M数据值（并且正在增长）需要大约 10分钟来提取59列的表格。我知道先前的软件需要1个小时来提取数据。

感谢您耐心阅读，直至此处：）

更新

在Denis回答后，我尝试了他的更改1.和2.，这是新查询的结果：

SELECT datetime, MAX(v1) AS v1, MAX(v2) AS v2, MAX(v3) AS v3 FROM (

SELECT acq.datetime AS datetime, data.value AS v1, NULL AS v2, NULL AS v3 
FROM acq INNER JOIN data ON acq.id = data.id_acq
WHERE acq.id_cu = 3 AND data.id_meas = 2 AND data.id_elab = 1
AND datetime >= "2011-03-01 00:00:00" AND datetime <= "2011-04-30 23:59:59"

UNION ALL

SELECT acq.datetime AS datetime, NULL AS v1, data.value AS v2, NULL AS v3 
FROM acq INNER JOIN data ON acq.id = data.id_acq
WHERE acq.id_cu = 5 AND data.id_meas = 4 AND data.id_elab = 6
AND datetime >= "2011-03-01 00:00:00" AND datetime <= "2011-04-30 23:59:59"

UNION ALL

SELECT acq.datetime AS datetime, NULL AS v1, NULL AS v2, data.value AS v3 
FROM acq INNER JOIN data ON acq.id = data.id_acq
WHERE acq.id_cu = 7 AND data.id_meas = 9 AND data.id_elab = 8
AND datetime >= "2011-03-01 00:00:00" AND datetime <= "2011-04-30 23:59:59"

) AS T GROUP BY datetime

这里是新的EXPLAIN EXTENDED：

+----+--------------+--------------+-------+--------------------------------------------------------------+----------------+---------+------------------------+-------+----------+---------------------------------+
| id | select_type  | table        | type  | possible_keys                                                | key            | key_len | ref                    | rows  | filtered | Extra                           |
+----+--------------+--------------+-------+--------------------------------------------------------------+----------------+---------+------------------------+-------+----------+---------------------------------+
|  1 | PRIMARY      | <derived2>   | ALL   | NULL                                                         | NULL           | NULL    | NULL                   | 51997 |   100.00 | Using temporary; Using filesort |
|  2 | DERIVED      | acquisitions | range | PRIMARY,id_cu,ix_acquisitions_datetime,ix_acquisitions_id_cu | id_cu          | 12      | NULL                   | 14827 |   100.00 | Using where                     |
|  2 | DERIVED      | data         | ref   | ix_data_id_meas,ix_data_id_acq,ix_data_id_elab               | ix_data_id_acq | 4       | sensor.acquisitions.id |     9 |   100.00 | Using where                     |
|  3 | UNION        | acquisitions | range | PRIMARY,id_cu,ix_acquisitions_datetime,ix_acquisitions_id_cu | id_cu          | 12      | NULL                   | 18663 |   100.00 | Using where                     |
|  3 | UNION        | data         | ref   | ix_data_id_meas,ix_data_id_acq,ix_data_id_elab               | ix_data_id_acq | 4       | sensor.acquisitions.id |     9 |   100.00 | Using where                     |
|  4 | UNION        | acquisitions | range | PRIMARY,id_cu,ix_acquisitions_datetime,ix_acquisitions_id_cu | id_cu          | 12      | NULL                   | 13260 |   100.00 | Using where                     |
|  4 | UNION        | data         | ref   | ix_data_id_meas,ix_data_id_acq,ix_data_id_elab               | ix_data_id_acq | 4       | sensor.acquisitions.id |     9 |   100.00 | Using where                     |
| NULL | UNION RESULT | <union2,3,4> | ALL   | NULL                                                         | NULL           | NULL    | NULL                   |  NULL |     NULL |                                 |
+----+--------------+--------------+-------+--------------------------------------------------------------+----------------+---------+------------------------+-------+----------+---------------------------------+
8 rows in set, 1 warning (3.01 sec)

毫无疑问，

表现良好的表现

更新（2）

这会添加点3.

EXPLAIN EXTENDED SELECT datetime, MAX(v1) AS v1, MAX(v2) AS v2, MAX(v3) AS v3 FROM (

SELECT acquisitions.datetime AS datetime, MAX(data.value) AS v1, NULL AS v2, NULL AS v3 
FROM acquisitions INNER JOIN data ON acquisitions.id = data.id_acq
WHERE acquisitions.id_cu = 1 AND data.id_meas = 1 AND data.id_elab = 2
AND datetime >= "2011-03-01 00:00:00" AND datetime <= "2011-04-30 23:59:59"
GROUP BY datetime

UNION ALL

SELECT acquisitions.datetime AS datetime, NULL AS v1, MAX(data.value) AS v2, NULL AS v3 
FROM acquisitions INNER JOIN data ON acquisitions.id = data.id_acq
WHERE acquisitions.id_cu = 4 AND data.id_meas = 1 AND data.id_elab = 2
AND datetime >= "2011-03-01 00:00:00" AND datetime <= "2011-04-30 23:59:59"
GROUP BY datetime

UNION ALL

SELECT acquisitions.datetime AS datetime, NULL AS v1, NULL AS v2, MAX(data.value) AS v3 
FROM acquisitions INNER JOIN data ON acquisitions.id = data.id_acq
WHERE acquisitions.id_cu = 8 AND data.id_meas = 1 AND data.id_elab = 2
AND datetime >= "2011-03-01 00:00:00" AND datetime <= "2011-04-30 23:59:59"
GROUP BY datetime

) AS T GROUP BY datetime;

这是EXPLAIN EXTENDED

的结果

+----+--------------+--------------+-------+--------------------------------------------------------------+----------------+---------+------------------------+-------+----------+---------------------------------+
| id | select_type  | table        | type  | possible_keys                                                | key            | key_len | ref                    | rows  | filtered | Extra                           |
+----+--------------+--------------+-------+--------------------------------------------------------------+----------------+---------+------------------------+-------+----------+---------------------------------+
|  1 | PRIMARY      | <derived2>   | ALL   | NULL                                                         | NULL           | NULL    | NULL                   | 51997 |   100.00 | Using temporary; Using filesort |
|  2 | DERIVED      | acquisitions | range | PRIMARY,id_cu,ix_acquisitions_datetime,ix_acquisitions_id_cu | id_cu          | 12      | NULL                   | 14827 |   100.00 | Using where                     |
|  2 | DERIVED      | data         | ref   | ix_data_id_meas,ix_data_id_acq,ix_data_id_elab               | ix_data_id_acq | 4       | sensor.acquisitions.id |     9 |   100.00 | Using where                     |
|  3 | UNION        | acquisitions | range | PRIMARY,id_cu,ix_acquisitions_datetime,ix_acquisitions_id_cu | id_cu          | 12      | NULL                   | 18663 |   100.00 | Using where                     |
|  3 | UNION        | data         | ref   | ix_data_id_meas,ix_data_id_acq,ix_data_id_elab               | ix_data_id_acq | 4       | sensor.acquisitions.id |     9 |   100.00 | Using where                     |
|  4 | UNION        | acquisitions | range | PRIMARY,id_cu,ix_acquisitions_datetime,ix_acquisitions_id_cu | id_cu          | 12      | NULL                   | 13260 |   100.00 | Using where                     |
|  4 | UNION        | data         | ref   | ix_data_id_meas,ix_data_id_acq,ix_data_id_elab               | ix_data_id_acq | 4       | sensor.acquisitions.id |     9 |   100.00 | Using where                     |
| NULL | UNION RESULT | <union2,3,4> | ALL   | NULL                                                         | NULL           | NULL    | NULL                   |  NULL |     NULL |                                 |
+----+--------------+--------------+-------+--------------------------------------------------------------+----------------+---------+------------------------+-------+----------+---------------------------------+
8 rows in set, 1 warning (3.06 sec)

稍慢一点，这应该是从大量的coulmns中受益吗？我会试试......

更新（3）

我尝试使用和不使用MAX(data.value)... GROUP BY datetime，在60列查询中，我获得了更好的结果。结果因尝试而异，这是其中之一。

原始查询9m12.144s
与Denis'1.和2. 4m6.597s
与Denis'1.，2.和3. 4m0.210s

所需时间减少约57％。

更新（4）

我尝试过Andiry解决方案，但它比Denis优化要慢。

测试了3个组合 / columns：

未优化：1m3s
Denis'优化：1.7s
Andiry的CASE：9.3s

我还测试了12个组合 / columns：

未经优化：未经测试
Denis'优化：3.6s
Andiry的CASE：13.7s

此外，Andiry的解决方案还包括收购日期，其中没有任何所选组合的数据，但存在于其他组合。

Immagine控制单元1每隔30分钟在00和30获取数据，而控制单元2在：15和45：我将使用NULL填充空行的行数加倍。

注意：

所有关于传感器系统：有几个控制单元</ strong>（每个id_cu一个），每个传感器。

单个传感器由id_cu / id_meas对标识，并为每个度量发送不同的详细说明，例如MIN（id_elab=1），MAX（id_elab=2）， AVERAGE（id_elab=3），INSTANT（id_elab=...）等，每个id_elab一个。

用户可以自由地接收他想要的许多详细说明，例如：

结果列的控制单元＃1的传感器＃3的平均值（3）id_cu=1 / id_meas=3 / id_elab=3

结果列的控制单元＃1的传感器＃5的平均值（3）id_cu=1 / id_meas=5 / id_elab=3

另一列控制单元＃4的传感器＃2的MIN值（1）id_cu=4 / id_meas=2 / id_elab=1

（放置任何有效的id_cu, id_meas, id_elab组合）

...

等等，多达数十种选择......

这是部分DDL（不包括不相关的表格）：

CREATE TABLE acquisitions ( id INTEGER NOT NULL AUTO_INCREMENT, id_cu INTEGER NOT NULL, datetime DATETIME NOT NULL, PRIMARY KEY (id), UNIQUE (id_cu, datetime), FOREIGN KEY(id_cu) REFERENCES ctrl_units (id) ON DELETE CASCADE ) CREATE TABLE data ( id INTEGER NOT NULL AUTO_INCREMENT, id_acq INTEGER NOT NULL, id_meas INTEGER NOT NULL, id_elab INTEGER NOT NULL, value FLOAT, PRIMARY KEY (id), FOREIGN KEY(id_acq) REFERENCES acquisitions (id) ON DELETE CASCADE ) CREATE TABLE ctrl_units ( id INTEGER NOT NULL, name VARCHAR(40) NOT NULL, PRIMARY KEY (id) ) CREATE TABLE sensors ( id_cu INTEGER NOT NULL, id_meas INTEGER NOT NULL, id_elab INTEGER NOT NULL, name VARCHAR(40) NOT NULL, `desc` VARCHAR(80), PRIMARY KEY (id_cu, id_meas), FOREIGN KEY(id_cu) REFERENCES ctrl_units (id) ON DELETE CASCADE )

Answer 1

主要有三个问题：

使用union all，而不是union。您正在对最小/最大值进行分组和提取，因此引入排序步骤以删除重复行没有意义。
where子句可以放在每个联合子语句中：
```
select ...
from (
select ... from ...  where ...
union all
select ... from ...  where ...
union all
...
)
group by ...
```
你编写它的方式，首先是获取所有行，然后将它们全部附加，最后过滤掉你需要的行。在union子语句中注入where子句将使其仅获取所需的行，最后将它们全部附加。

同样，预聚合聚合：

select ..., max(foo) as foo
from (
select ..., max(foo) as foo from ...  where ... group by ...
union all
select ..., max(foo) as foo from ...  where ... group by ...
union all
...
)
group by ...

优化器将更好地利用现有索引，并且最终只会添加几行，而不是数百万行。

Answer 2

SELECT
  acq.datetime,
  MAX(CASE WHEN acq.id_cu = 2 AND data.id_meas = 2 AND data.id_elab = 1 THEN data.value END) AS v1,
  MAX(CASE WHEN acq.id_cu = 5 AND data.id_meas = 4 AND data.id_elab = 6 THEN data.value END) AS v2,
  MAX(CASE WHEN acq.id_cu = 7 AND data.id_meas = 9 AND data.id_elab = 8 THEN data.value END) AS v3
FROM acq
  INNER JOIN data acq.id = data.id_acq
WHERE datetime >= 2011-03-01 00:00:00 AND datetime <= 2011-04-30 23:59:59
GROUP BY acq.datetime

这可能看起来与原始查询大致相同，但主要区别在于逻辑上它只扫描一次表而不是三次或多次使用UNIONs。

Answer 3

基本上我认为使用单个SELECT和CASE处理条件会得到更好的结果。无论如何，您可能想要进行基准测试和比较......

SELECT acq.datetime AS datetime, 
       MAX(
           CASE acq.id_cu
           WHEN 1 THEN data.value
           END 
       ) as v1,
       MAX(
           CASE acq.id_cu
           WHEN 4 THEN data.value
           END 
       ) as v2,
       MAX(
           CASE acq.id_cu
           WHEN 8 THEN data.value
           END 
       ) as v3
FROM 
       acq INNER JOIN data ON acq.id = data.id_acq
WHERE 
       data.id_meas = 1 AND data.id_elab = 2 AND
       datetime BETWEEN "2011-03-01 00:00:00" AND "2011-04-30 23:59:59"

这应该进行清洁范围扫描。此外，复合索引可以做得更多。

最后，使用GROUP BY有什么问题，例如

SELECT data.id_means, acq.datetime AS datetime, MAX(data.value)
FROM 
       acq INNER JOIN data ON acq.id = data.id_acq
WHERE 
       data.id_elab = 2 AND
       datetime BETWEEN "2011-03-01 00:00:00" AND "2011-04-30 23:59:59" AND
       data.id_means IN (1,4,8)
GROUP BY
       data.id_means

这是最简单的形式（也是最灵活的） - 即使行没有为您调换行（对于data.id_meas的不同值）。但是，这将使您最好地了解期望的性能以及哪些索引对查询最有用。

修改要获得* acq.id_cu的最大数据值 - data.id_meas - data.id_elab组合*您应该能够使用

SELECT acq.id_cu, data.id_meas, data.id_elab, acq.datetime AS datetime, MAX(data.value) FROM acq INNER JOIN data ON acq.id = data.id_acq WHERE data.id_elab = 2 AND datetime BETWEEN "2011-03-01 00:00:00" AND "2011-04-30 23:59:59" AND data.id_means IN (1,4,8) GROUP BY acq.id_cu, data.id_meas, data.id_elab, acq.datetime

将为acq.id_cu, data.id_meas, data.id_elab, acq.datetime的所有组合提供max（data.value）（在过滤后使用其中的值 - 调整影响结果的位置）。对于没有行的组合，这不会显示NULL，但如果这是适合您的方向，则有一种解决方法。 GROUP BY也确定排序，因此更改group by中的列顺序。

如果我的答案仍然缺失，那么一些样本数据/测试用例会很有用。

你的例子中令人困惑的部分就是当你说
时

每列对应data.value 对于选定的acq.id_cu - data.id_meas - data.id_elab组合。

但是当您在示例查询中选择数据时，您可以直接将它们选择为仅具有日期时间分组的列，因此如果它实际上是值的组合，则无法识别哪个行对应于哪个组合（可能有多个行）某某日期）。如果它不是您要过滤/分组的所有值的组合，但确定max值的分组条件直接取决于datetime。

优化从同一个表中提取的多个列的查询

更新

更新（2）

更新（3）

更新（4）

3 个答案: