Question

Lets say I have a table of statisctics:

Page | Action | Time
--------------------
Home | Logon  |  12
Home | Logon  |  11
Home | Search |  20
About| Comment|  10

I can write a query to get the average Action time for each page:

select Page, avg(Time) from statistics group by Page

But I’d like to be a bit more clever. In order to highlight which pages have the most slow actions on, I’d like to get the sum of (time – average time for all actions on all pages). I could do this in separate queries:

select avg(Time) from statistics
-> 15
select Page, sum(Time - 15) from statistics group by Page

Question is, is there a way to do this in a single query?

Obviously select Page, sum(Time - avg(Time)) from statistics group by Page doesn’t work. Oracle throws “ORA-00937: not a single-group group function”.

Answer 1

You could use Window functions:

SELECT  DISTINCT 
        Page, 
        AVG(Time) OVER(PARTITION BY Page) - AVG(Time) OVER() AS Variance
FROM    Statistics

And to expand slightly you can then get many different averages in the one query:

SELECT  Page, 
        Action,
        Time,
        AVG(Time) OVER(PARTITION BY Page, Action) AS AverageActionTime,
        AVG(Time) OVER(PARTITION BY Page) AS AveragePageTime,
        AVG(Time) OVER() AS AverageTime
FROM    Statistics

http://sqlfiddle.com/#!4/42a5f/8