如何根据字符串b的值在时间刻度DB中查询新的整数值？

Question

我有一个名为 metric 的时间刻度数据库，其中存储了许多不同的参数，有些是字符串值，有些是整数值。基本上，我有一个名为“carbon”的参数，它是一个整数值，我有一个名为“stationName”的字符串值。此查询的目标是仅当 stationName 等于“ST2”时显示给定时间段内的碳值。任何有关如何完成此操作的帮助将不胜感激，因为这是我第一次处理时间序列查询。

下面我添加了到目前为止我尝试过的示例查询和数据库的架构。

数据库架构

timestamp - 时间戳值

参数 - 参数名称

data_text - 当参数是文本类型时使用

data_float - 当参数为数字时使用

    WITH
 -- a and b are for reading data 

a AS ( SELECT 
    timestamp AS t, 
    data_float AS carbon 
  FROM 
    metric 
  WHERE 
    parameter = 'db.C' 
    AND timestamp BETWEEN $START_TIME::timestamp AND $END_TIME
),
 
b AS (
  SELECT
    timestamp AS t,
    data_text AS station
  FROM metric
  WHERE parameter = 'db.StationName'
  AND timestamp BETWEEN $START_TIME::timestamp AND $END_TIME
),
 
c AS (
  SELECT t, carbon, NULL AS station FROM a 
  UNION ALL
  SELECT t, NULL AS carbon, station FROM b
),
 
d AS (
  SELECT *,
         COUNT(carbon) OVER (ORDER BY t) AS grp
  FROM c
),
e AS (
  SELECT t, 
         carbon AS carbon_val, 
         station AS station_val
  FROM d
)
 
SELECT 
  t AS timestamp, 
  carbon_val,
  station_val,
  'db.C_for_ST2' As columns
FROM e
WHERE 
  station_val = "ST2"
  AND t BETWEEN $START_TIME AND $END_TIME```

Answer 1

我会开始将它们分解为视图，以使问题更容易解决：

create view station_events as
 SELECT
    timestamp AS t,
    data_text AS station
FROM metric
  WHERE parameter = 'db.StationName'

碳事件也一样：

create view carbon_events as SELECT 
    timestamp AS t, 
    data_float AS carbon 
  FROM 
    metric;

现在，用 CTE 来过滤电台：

WITH the_station AS
(select * from station_events where station = 'ST2' and BETWEEN $START_TIME::timestamp AND $END_TIME)
SELECT station, (select count(*) FROM carbon_events WHERE carbon_events.time BETWEEN the_station.time and $END_TIME)) as carbon_count from the_station;

我不确定查询是否正确，我受到这个主题的启发来回答最后一部分：PostgreSQL：加入另一个表的计数

您还可以考虑使用更高级的组件，例如状态跟踪。