Question

我有这个数据库存储传感器采集数据，
采购（acq）来自不同的控制单元（cu），固定间隔（日期时间）
每个采集都有许多不同的度量存储在数据表

中

acq
    id  
    datetime 
    id_cu     

data          
    id        
    id_acq  
    id_meas
    value

我需要这种观点：

+---------------------+------+----+-----+
|      datetime       |  v1  | v2 |  v3 |
+---------------------+------+----+-----+
| 2010-09-13 00:05:00 | 40.9 |  1 | 0.3 |
| 2010-09-13 00:10:00 | 41.0 |  2 | 0.3 |
| 2010-09-13 00:15:00 | 41.1 |  4 | 0.3 |
+---------------------+------+----+-----+

AS：

v1是data.value（例如湿度）
WHERE acq.id_cu = 1 AND data.id_meas = 100
v2是data.value（例如计数器）
WHERE acq.id_cu = 2 AND data.id_meas = 200
v3是data.value（例如温度）
WHERE acq.id_cu = 3 AND data.id_meas = 300

以及用户选择的几十种组合

我最终得到了这个查询，但与生产中的数据相比，它只需要很少的数据

SELECT a1.datetime, d1.value, d2.value, d3.value
FROM
    acq a1, data d1
    JOIN acq a2, data d2
        ON a2.id=d2.id_acq AND a2.datetime=a1.datetime
    JOIN acq a3, data d3
        ON a3.id=d3.id_acq AND a3.datetime=a1.datetime
WHERE a1.id=d1.id_acq
    AND a1.id_cu=1 AND d1.id_meas=100
    AND a2.id_cu=2 AND d2.id_meas=200
    AND a3.id_cu=3 AND d3.id_meas=300

我想，对于每个a1.id_centr=x AND d1.id_meas=y条件单独获取数据然后以我想要的方式打印数据表会更快。

实现这一目标的最佳（和正确）方法是什么？

编辑：假设不缺少收购，我的意思是运行：

SELECT datetime, value
FROM acq, data
WHERE acq.id=data.id_acq
    AND (
        id_cu=1 AND id_meas=100
        OR id_cu=2 AND id_meas=200
        OR id_cu=3 AND id_meas=300
    )
ORDER BY id_cu, id_meas

通过id_cu / id_meas改变并使用编程语言（如python + numpy）并排显示结果的分割结果是几秒钟与......分钟的关系？

Answer 1

*假设DATETIME和data.id_acq以及cu和id_meas都有索引*，您可以尝试使用虚拟列占位符和kludgey MAX（）的UNION查询。如果你的data.values不是负数，那么它应该有效（如果它们你可以简单地选择一个非常大的负数而不是零作为虚拟占位符值，这个数字远远超出可能的范围）：

    select FOO.datetime, max(FOO.v1), max(FOO.v2), max(FOO.v3)
    from
     (

     select acq.datetime, data.value as v1,0 as v2, 0 as v3
     from acq inner join data on acq.id = data.id_acq
     where acq.id_cu=1 and data.id_meas=100

     UNION

    select acq.datetime, 0 as v1, data.value as v2, 0 as v3
    from acq inner join data on acq.id = data.id_acq
    where acq.id_cu=2 and data.id_meas=200

    UNION

    select acq.datetime, 0 as v1, 0 v2, data.value as v3
    from acq inner join data on acq.id = data.id_acq
    where acq.id_cu=3 and data.id_meas=300
    ) as FOO
    group by FOO.datetime

Answer 2

你的JOINS有点令人困惑（因为你在暗示中混合显式）;试试这个：

SELECT a1.datetime, d1.value, d2.value, d3.value
FROM
    acq a1 
       INNER JOIN data d1 ON a1.id=d1.id_acq
       INNER JOIN acq a2  ON a2.datetime=a1.datetime
       INNER JOIN data d2 ON a2.id=d2.id_acq
       INNER JOIN acq a3  ON a3.datetime=a1.datetime
       INNER JOIN data d3 ON a3.id=d3.id_acq
WHERE 1=1
    AND a1.id_centr=1 AND d1.id_meas=100
    AND a2.id_centr=2 AND d2.id_meas=200
    AND a3.id_centr=3 AND d3.id_meas=300

同一个表上的多个JOIN视图

2 个答案: