Average of a field by date by site

Question

Our data source has multiple records for a single day (date time stamped) for multiple sites.
For example:
SiteID, Date, Time, CH4
With a record every few minutes.
We need to calculate the average of CH4 for a single day (Date) for each Site (SiteID). The following CTE gets me the most recent value:
WITH GasEngine_CTE 
AS
SELECT CH4, ROW_NUMBER() OVER(PARTITION BY SiteID ORDER BY CAST([Date] AS DATETIME) + CAST([Time] AS DATETIME) DESC) RowNumber
FROM dbo.GasEngine
SELECT *
FROM GasEngine_CTE 
WHERE RowNumber = 1
I need to modify to retrieve the average for each day and each site. I think I need to group (partition) by SiteID and [Date]

Answer 1

Is that you are looking for?
declare @gasengine table(ch4 int, site varchar(2), dt date);
insert into @gasengine
values(1,'S1',getdate()),
(3,'S1',getdate()),
(3,'S1',getdate()-1),
(5,'S1',getdate()-1);
SELECT Site,dt,Avg(CH4)
FROM @gasengine
group by [Site],[Dt]
Satheesh
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