I am using PostgreSQL.
I have a table like below:
ID product_id Date Qty
-----------------------------------
1 12 2008-06-02 50
2 3 2008-07-12 5
3 12 2009-02-10 25
4 10 2012-11-01 22
5 2 2011-03-25 7
Now I want the result like below (i.e product wise sum of qty field of last 4 years):
product_id
QTY(current_year)
QTY( current year + last_year)
QTY_last2_years
QTY > 2 years
SELECT product_id
,sum(CASE mydate >= x.t THEN qty END) AS qty_current_year
,sum(CASE mydate >= (x.t - interval '1 y') THEN qty END) AS qty_since_last_year
,sum(CASE mydate >= (x.t - interval '2 y')
AND mydate < x.t THEN qty END) AS qty_last_2_year
,sum(CASE mydate < (x.t - interval '2 y') THEN qty END) AS qty_older
FROM tbl
CROSS JOIN (SELECT date_trunc('year', now()) AS t) x -- calculate once
GROUP BY 1;
To resuse the calculated beginning of the current year I CROSS JOIN it as subquery x.
