Question

I’m trying to generate a SQL query to extract an average montly powerusage (of a year) for an ID.

+----+------------+------------+
| id | powerusage |    date    |
+----+------------+------------+
|  1 |        750 | 2011-12-2  |
|  1 |       1000 | 2011-12-1  |
|  1 |       1500 | 2011-11-15 |
|  1 |        100 | 2011-11-13 |
|  1 |         50 | 2011-11-10 |
|  2 |        500 | 2011-11-15 |
|  2 |        200 | 2011-11-13 |
+----+------------+------------+

So if ID = 1 I want (avg november + avg december) / 2 = (1750/2 + 1650/3) / 2 = 712.5

select AVG(powerusage) as avgMontlyPowerUsage
from usagetable 
where id = 1 and YEAR(date) = 2011

But this will give me 680.

How do I do a average on a group?

Many thanks for all the answers! But I see my question is incorrect. See updated question

Answer 1

Something like

select AVG(montlyPowerUsage) from (

SELECT MONTH(date) as mnth,sum(powerusage) as montlyPowerUsage
from usagetable 
where id = 1 and YEAR(date) = 2011 group by MONTH(date)

) t1

For Edited question

select AVG(montlyPowerUsage) from (

SELECT MONTH(date) as mnth,AVG(powerusage) as montlyPowerUsage
from usagetable 
where id = 1 and YEAR(date) = 2011 group by MONTH(date)

) t1