Querying average and rolling 12 month average - sql

Question

I want to be able to find out the average per month and rolling average over the last 12 months of a count for the number of changes per customer.
SELECT
crq_requested_by_company as 'Customer',
COUNT(crq_number) as 'Number of Changes'
FROM
change_information ci1
GROUP BY
crq_requested_by_company
At the moment I am just doing the count of the total and my results look like this
crq_requested_by_company count
A 4
B 2
C 2269
D 7696
E 110
F 91
G 33
The date column I will be using is called 'start_date'.
I assume GETDATE() will be needed to work out the rolling average for the last 12 months.
Additional info after comments:
Using the code
;WITH CTE as
(
SELECT
crq_requested_by_company as Customer,
COUNT(crq_number) Nuc,
dateadd(month, datediff(month, 0, crq_start_date),0) m
FROM
change_information ci1
WHERE
crq_start_date >= dateadd(month,datediff(month, 0,getdate()) - 12,0)
GROUP BY
crq_requested_by_company,
datediff(month, 0, crq_start_date)
)
SELECT
Customer,
avg(Nuc) over (partition by Customer order by m) running_avg,
m start_month,
avg(Nuc) over (partition by Customer) simply_average
FROM
CTE
ORDER BY Customer, start_month
This gives the results
Customer running_avg start_month simply_average
A 8 01/01/2016 00:00 13
A 10 01/02/2016 00:00 13
A 10 01/03/2016 00:00 13
A 11 01/04/2016 00:00 13
A 14 01/05/2016 00:00 13
A 13 01/06/2016 00:00 13
B 1 01/01/2016 00:00 1
C 3 01/01/2016 00:00 2
C 3 01/02/2016 00:00 2
C 2 01/03/2016 00:00 2
C 2 01/04/2016 00:00 2
C 2 01/05/2016 00:00 2
C 2 01/06/2016 00:00 2
It needs to look like this so the average of the results above - the average of the 6 months above (I only currently have 6 months of data and needs to be 12 eventually)
Customer avg_of_running_avg
A 11
B 1
C 2

Answer 1

Try this, it should work for sqlserver 2012 using running average:
;WITH CTE as
(
SELECT
crq_requested_by_company as Customer,
COUNT(crq_number) Nuc,
dateadd(month, datediff(month, 0, start_date),0) m
FROM
change_information ci1
WHERE
start_date >= dateadd(month,datediff(month, 0,getdate()) - 12,0)
GROUP BY
crq_requested_by_company,
datediff(month, 0, start_date)
)
SELECT
Customer,
avg(Nuc) over (partition by Customer order by m) running_avg,
m start_month,
avg(Nuc) over (partition by Customer) simply_average
FROM
CTE
ORDER BY Customer, start_month