Postgres平均时间数据

Question

我们使用Postgres来记录来自我们流程的数据。我们的数据库的一个例子如下：

CREATE TABLE Data 
("time_stamp" timestamp, "pressure" numeric, "temperature" numeric, "flow" numeric); 

INSERT INTO Data 
("time_stamp", "pressure", "temperature", "flow") 
VALUES 
('2016-05-12 20:42:24', 97.68, 9.02564, 2.24664), 
('2016-05-12 20:42:25', 97.68, 9.02564, 2.24054), 
('2016-05-12 20:42:26', 122.1, 9.01832, 2.24054), 
('2016-05-12 20:42:27', 122.1, 9.01099, 2.23443), 
('2016-05-12 20:42:28', 97.68, 9.01099, 2.23443), 
('2016-05-12 20:42:29', 122.1, 9.01099, 2.24054), 
('2016-05-12 20:42:30', 97.68, 9.01099, 2.23443), 
('2016-05-12 20:42:31', 122.1, 9.01099, 2.23443), 
('2016-05-12 20:42:32', 122.1, 9.01832, 2.24054), 
('2016-05-12 20:42:33', 122.1, 9.01832, 2.23443); 

我所试图做的就是Postgres的（使用pgAdminIII）来生成一个任意时间片的平均数据，比如5秒。它会输出一个平均的时间，压力，温度和流量列这五秒钟。该数据将有两个条目，时间条目为'2016-05-12 20:42:26'和'2016-05-12 20:42:31'。

Answer 1

下面是一个解决方案，这不是最好的，但有点作品。

SELECT timestamp without time zone '1970-01-01' + cast(avg(extract(epoch from time_stamp))::text as interval), 
     sub.press, 
     sub.temp, 
     sub.flow 
FROM data d join (
    SELECT 
      (extract(seconds from time_stamp)/5)::integer as num, 
      avg(pressure) as press, 
      avg(temperature) as temp, 
      avg(flow) as flow 
     FROM 
      data 
     group by 1) sub on sub.num=(extract(second from d.time_stamp)/5)::integer 
group by sub.press,sub.temp,sub.flow 
order by 1 

子选择从数据表中选择数据并将其分组5秒。时间戳需要外部选择才能获得“平均”。我认为这对功能来说应该更容易。

编辑： 这是我为此写的功能。假设每秒只有一行。

您需要首先创建一个自定义类型：

CREATE TYPE t_data AS 
(
    time_stamp timestamp, 
    pressure numeric, 
    temp numeric, 
    flow numeric); 

这是函数：

CREATE OR REPLACE FUNCTION dataCheck (timeInterval integer) RETURNS setof t_data AS $BODY$ 
DECLARE 
    pressure numeric[]; 
    temp numeric[]; 
    flow numeric[]; 
    rec record; 
    i integer default 1; 
    ret t_data; 
BEGIN 
    for rec in select * from data order by time_stamp 
    loop 
    pressure[i]=rec.pressure; 
    temp[i]=rec.temp; 
    flow[i]=rec.flow; 

    if i=(timeInterval/2 + case when timeInterval%2 <> 0 then 1 else 0 end) then 
     ret.time_stamp=rec.time_stamp; 
    end if; 
    if i=timeInterval then 
     i=0; 
     ret.pressure=avg((select avg(a) from unnest(pressure) as a)); 
     ret.temp=avg((select avg(a) from unnest(temp) as a)); 
     ret.flow=avg((select avg(a) from unnest(flow) as a)); 
     return next ret; 
    end if; 

    i=i+1; 
    end loop; 

return ; 

end;$BODY$ LANGUAGE plpgsql; 

这就是你如何执行它：

SELECT * from dataCheck(5); 

的功能每“5”行返回平均数据。