具有多行的SQL聚合

Question

我有以下查询

SELECT tagindex, AVG(val) from floatTable
 WHERE tagindex IN(828,856,883,910)
   AND DateAndTime > DATEADD(HH,-1,GETDATE()) 
   AND DateAndTime < DATEADD(HH,-2,GETDATE())
group by tagindex

返回以下内容：

828   1
856   1
883   1
910   1

如果它是所有行的组合平均值，我如何返回单个结果？

Answer 1

SELECT AVG(val) 
FROM floatTable 
WHERE tagindex IN (828, 856, 883, 910) 
    AND DateAndTime > DATEADD(HH, -1, GETDATE()) 
    AND DateAndTime < DATEADD(HH, -2, GETDATE()) 

Answer 2

Select Avg(AverageValue)
From
(
   SELECT tagindex, AVG(val) as AverageValue from floatTable
   WHERE tagindex IN(828,856,883,910)
   AND DateAndTime > DATEADD(HH,-1,GETDATE()) AND DateAndTime < DATEADD(HH,-2,GETDATE())
   group by tagindex
) AverageValues