Re : Get Average count of previous 3 Years

Question

Hello All,
Hope all is well. I have this query , where I am counting the numbers of items sold based on 4 dimensions and then in the next column now client wants the average count of previous 3 years items sold.
The query results look like this ,
Year Office item_type count_items_Curr_Year count_items_pre_3yrs
My current simple SQL looks like ,
select Year, Office, item_type,count(item_id)
from Years,
Offices,
Item_types
group by Year, Office, item_type
Could someone help me create query for to calculate the average count of previous 3 years items sold.
For example,
Year-----Office-----item_type-----count_items_Curr_Year-----count_items_pre_3yrs
2000-----ABC------Jewellery-------100------------------------------------95(Avg. count of 1999,1998,1997)
2001-----ABC------Sports-------250------------------------------------260(Avg. count of 2000,1999,1998)
2002-----XYZ------Sports-------350------------------------------------288(Avg. count of 2001,2000,1999)
2003-----FCD------Auto-------500------------------------------------387(Avg. count of 2002,2001,2000)
and so on......
I hope I am clear on this . Please let me know if I have missed on something.
Thanks in advance,
Sam

Answer 1

You could do this using analytic functions, something like -
(untested) -
select year, office, item_type, cnt, avg(cnt) over (order by justyear desc range 3 preceding)
from
select to_char(year,'YYYY') justyear, Year, Office, item_type,count(item_id) cnt
from Years,
Offices,
Item_types
group by Year, Office, item_type, to_char(year,'YYYY')
left justyear out of the group by
Message was edited by:
stellios.k