多个列和空值中每行的SQL平均值

我有一个记录传感器数据的应用程序，我希望能够从多个传感器中得出平均值，可以是一个、两个、三个或更多

编辑：这些是温度传感器，因此0是传感器可能存储在数据库中的值

我最初的出发点是以下SQL查询：

SELECT grid.t5||'.000000' as ts,
avg(t.sensorvalue)  sensorvalue1
, avg(w.sensorvalue)AS sensorvalue2
FROM 
(SELECT generate_series(min(date_trunc('hour', ts))                         
,max(ts), interval '5 min') AS t5   FROM device_history_20865735 where      
 ts between '2015/05/13 09:00' and '2015/05/14 09:00'   ) grid 

 LEFT JOIN device_history_20865735 t ON t.ts >= grid.t5 AND t.ts <  grid.t5 +  interval '5 min' 
 LEFT JOIN device_history_493417852 w ON w.ts >= grid.t5 AND w.ts <  grid.t5 +  interval '5 min' 
--WHERE t.sensorvalue notnull
GROUP  BY grid.t5 ORDER  BY grid.t5

我的目标是计算所有可用传感器每5分钟间隔的平均值，因此空值是一个问题，我考虑使用CASE语句，因此如果存在空值，则获取其他传感器的值

SELECT grid.t5||'.000000' as ts,
CASE 
        WHEN avg(t.sensorvalue) ISNULL  THEN avg(w.sensorvalue)
        ELSE avg(t.sensorvalue)
END AS sensorvalue
,
CASE 
        WHEN avg(w.sensorvalue) ISNULL  THEN avg(t.sensorvalue)
        ELSE avg(w.sensorvalue)
END AS sensorvalue2
FROM 
(SELECT generate_series(min(date_trunc('hour', ts)),max(ts), interval '5 min') AS t5
FROM device_history_20865735 where      
 ts between '2015/05/13 09:00' and '2015/05/14 09:00'   ) grid 

 LEFT JOIN device_history_20865735 t ON t.ts >= grid.t5 AND t.ts <  grid.t5 +  interval '5 min' 
 LEFT JOIN device_history_493417852 w ON w.ts >= grid.t5 AND w.ts <  grid.t5 +  interval '5 min' 
GROUP  BY grid.t5 ORDER  BY grid.t5

但是为了计算平均值，我必须在这上面做另一个选择，并且每列数选择一个传感器，如果它们只有两个，这是可以的，但是如果有3个或4个传感器，这会变得非常混乱，因为可能有多个传感器每行都有空值

SQL是从使用postgres 9.4的Python应用程序语法上派生出来的，所以有没有一种简单的方法来实现我所需要的，因为我觉得我正在走一条相当复杂的道路

编辑2：根据您的输入，我已经生成了这段SQL代码，同样，它看起来相当复杂，但如果它可靠且可维护，则可以接受您的想法和审查：

SELECT ts, sensortotal, sensorcount,
CASE
    WHEN sensorcount = 0 THEN -1000
    ELSE sensortotal/sensorcount
END AS sensorAvg

FROM (
    WITH grid as (
          SELECT t5
          FROM (SELECT generate_series(min(date_trunc('hour', ts)), max(ts), interval '5 min') as t5
                FROM device_history_20865735
               ) d
          WHERE t5 between '2015-05-13 09:00' and '2015-05-14 09:00'   
         )
    SELECT d1.t5 || '.000000' as ts
           , Coalesce(avg(d1.sensorvalue), 0) + Coalesce(avg(d2.sensorvalue),0) as sensorTotal
           , (CASE
                    WHEN avg(d1.sensorvalue) ISNULL THEN 0
                    ELSE 1
           END + CASE
            WHEN avg(d2.sensorvalue) ISNULL THEN 0
            ELSE 1
           END) as sensorCount

    FROM (SELECT grid.t5, avg(t.sensorvalue) as sensorvalue
          FROM grid LEFT JOIN
               device_history_20865735 t
               ON t.ts >= grid.t5 AND t.ts <grid.t5 +  interval '5 min' 
          GROUP BY grid.t5
         ) d1 LEFT JOIN
         (SELECT grid.t5, avg(t.sensorvalue) as sensorvalue
          FROM grid LEFT JOIN
               device_history_493417852 t
               ON t.ts >= grid.t5 AND t.ts <grid.t5 +  interval '5 min' 
         GROUP BY grid.t5
         ) d2 on d1.t5 = d2.t5
    GROUP BY d1.t5
    ORDER BY d1.t5
) tmp;

---

谢谢

要获得准确的平均值，您需要在连接之前分别计算每个平均值：

WITH grid as (
      SELECT t5
      FROM (SELECT generate_series(min(date_trunc('hour', ts)), max(ts), interval '5 min') as t5
            FROM device_history_20865735
           ) d
      WHERE t5 between '2015-05-13 09:00' and '2015-05-14 09:00'   
     )
SELECT d1.t5 || '.000000' as ts,
       avg(d1.sensorvalue) as sensorvalue1
       , avg(d2.sensorvalue) as sensorvalue2
FROM (SELECT grid.t5, avg(t.sensorvalue) as sensorvalue
      FROM grid LEFT JOIN
           device_history_20865735 t
           ON t.ts >= grid.t5 AND t.ts <grid.t5 +  interval '5 min' 
      GROUP BY grid.t5
     ) d1 LEFT JOIN
     (SELECT grid.t5, avg(t.sensorvalue) as sensorvalue
      FROM grid LEFT JOIN
           device_history_493417852 t
           ON t.ts >= grid.t5 AND t.ts <grid.t5 +  interval '5 min' 
     GROUP BY grid.t5
     ) d2 on d1.t5 = d2.t5
GROUP BY d1.t5
ORDER BY d1.t5;

---

听起来你想做这样的事情：

(coalesce(value1,0) + coalesce(value2,0) + coalesce(value3,0)) /
(value1 IS NOT NULL::int + value2 IS NOT NULL::int + value3 IS NOT NULL::int)
AS average

基本上，只做你想为每一行做的数学题。唯一棘手的部分是如何计算非空值—我使用了强制转换，但还有其他选项，例如：

CASE WHEN value1 IS NULL THEN 0 ELSE 1 END

---

我不知道您需要如何计算平均值，但您可以执行coalescusmt.sensorvalue、0+coalescusmw.sensorvalue、0/countt.sensorvalue+countw.sensorvalue。这可以很容易地扩展到任何数量的传感器。谢谢@dnoeth！我需要按网格的每行计算一次，例如每5分钟一次，而不是整个列……谢谢@Gordon！-我得到一个语法错误，虽然。。。错误：第21行或其附近出现语法错误：GROUP BY d1.t5^左侧联接中的d1和d2之间没有关系，ON条件为缺失。我已设法使其运行，但结果与顶部的SQL相同。。。关于平均数问题，是否有更“优雅”的解决方案

CASE WHEN value1 IS NULL THEN 0 ELSE 1 END