SQL Aggregates OVER and PARTITION - sql

Question

All,
This is my first post on Stackoverflow, so go easy...
I am using SQL Server 2008.
I am fairly new to writing SQL queries, and I have a problem that I thought was pretty simple, but I've been fighting for 2 days. I have a set of data that looks like this:
UserId Duration(Seconds) Month
1 45 January
1 90 January
1 50 February
1 42 February
2 80 January
2 110 February
3 45 January
3 62 January
3 56 January
3 60 February
Now, what I want is to write a single query that gives me the average for a particular user and compares it against all user's average for that month. So the resulting dataset after a query for user #1 would look like this:
UserId Duration(seconds) OrganizationDuration(Seconds) Month
1 67.5 63 January
1 46 65.5 February
I've been batting around different subqueries and group by scenarios and nothing ever seems to work. Lately, I've been trying OVER and PARTITION BY, but with no success there either. My latest query looks like this:
select Userid,
AVG(duration) OVER () as OrgAverage,
AVG(duration) as UserAverage,
DATENAME(mm,MONTH(StartDate)) as Month
from table.name
where YEAR(StartDate)=2014
AND userid=119
GROUP BY MONTH(StartDate), UserId
This query bombs out with a "Duration' is invalid in the select list because it is not contained in either an aggregate function or the GROUP BY clause" error.
Please keep in mind I'm dealing with a very large amount of data. I think I can make it work with CASE statements, but I'm looking for a cleaner, more efficient way to write the query if possible.
Thank you!

Answer 1

You are joining two queries together here:
Per-User average per month
All Organisation average per month
If you are only going to return data for one user at a time then an inline select may give you joy:
SELECT AVG(a.duration) AS UserAvergage,
(SELECT AVG(b.Duration) FROM tbl b WHERE MONTH(b.StartDate) = MONTH(a.StartDate)) AS OrgAverage
...
FROM tbl a
WHERE userid = 119
GROUP BY MONTH(StartDate), UserId
Note - using comparison on MONTH may be slow - you may be better off having a CTE (Common Table Expression)

Answer 2

missing partition clause in Average function
OVER ( Partition by MONTH(StartDate))

Answer 3

Please try this. It works fine to me.
WITH C1
AS
(
SELECT
AVG(Duration) AS TotalAvg,
[Month]
FROM [dbo].[Test]
GROUP BY [Month]
),
C2
AS
(
SELECT Distinct UserID,
AVG(Duration) OVER(PARTITION BY UserID, [Month] ORDER BY UserID) AS DetailedAvg,
[Month]
FROM [dbo].[Test]
)
SELECT C2.*, C1.TotalAvg
FROM C2 c2
INNER JOIN C1 c1 ON c1.[Month] = c2.[Month]
ORDER BY c2.UserID, c2.[Month] desc;

Answer 4

I was able to get it done using a self join, There's probably a better way.
Select UserId, AVG(t1.Duration) as Duration, t2.duration as OrgDur, t1.Month
from #temp t1
inner join (Select Distinct MONTH, AVG(Duration) over (partition by Month) as duration
from #temp) t2 on t2.Month = t1.Month
group by t1.Month, t1.UserId, t2.Duration
order by t1.UserId, Month desc
Here's using a CTE which is probably a better solution and definitely easier to read
With MonthlyAverage
as
(
Select MONTH, AVG(Duration) as OrgDur
from #temp
group by Month
)
Select UserId, AVG(t1.Duration) as Duration, m.duration as OrgDur , t1.Month
from #temp t1
inner join MonthlyAverage m on m.Month = t1.Month
group by UserId, t1.Month, m.duration

Answer 5

You can try below with less code.
SELECT Distinct UserID,
AVG(Duration) OVER(PARTITION BY [Month]) AS TotalAvg,
AVG(Duration) OVER(PARTITION BY UserID, [Month] ORDER BY UserID) AS DetailedAvg,
[Month]
FROM [dbo].[Test]