同一张表上的多个JOIN视图

Question

我有这个数据库存储传感器采集数据，
采集（acq）来自不同控制单元（cu）的固定间隔（日期时间）
每个采集在数据表中存储了许多不同的度量

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 |
+---------------------+------+----+-----+

作为：

• v1是data.value（例如湿度），其中
  acq.id_cu = 1 AND data.id_meas = 100

• v2是data.value（例如计数器），其中
  acq.id_cu = 2 AND data.id_meas = 200

• v3是data.value（例如温度），其中
  acq.id_cu = 3 AND data.id_meas = 300

依此类推，用户最多可以选择数十种组合

我结束了此查询，但与将要生产的数据相比，它永久占用的数据量很少

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

我想这将是更快的方法，可以分别为每个a1.id_centr=x AND d1.id_meas=y条件获取数据，然后以我想要的方式打印应用程序中列出的数据。

实现这一目标的最佳（正确）方法是什么？

编辑：假设不缺乏收购我的意思是运行此：

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

由id_cu / id_meas进行的拆分结果会更改，并使用编程语言（如python + numpy）并排显示结果，这是几分之一秒还是……分钟？

Answer 1

假设DATETIME和data.id_acq以及cu和id_meas都有索引，则可以尝试使用带有伪列占位符和kludgey MAX（）的UNION查询。如果您的data.values不是负数，这应该可以工作（如果是，则可以选择一个非常大的负数而不是零作为虚拟占位符值，该数字远远超出了可能的范围）：

    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