Iterative function in SQL, postgres - sql

Question

I have a gigantic script that I would like to create in an iterative way (while or for loop), so it becomes overviewable and much shorter. It makes so much sense that it should be doable in SQL but so far I have not succeeded. What I did now in order to make it work is a lot of selections that I UNION together to make one table.
I want to iterate through the years, so while year is lower then 2017 execute function with the year in it as variable, starting from 1995.
So actually, an iterative function that fills in all years in the following lines of code and combines all results within one table: I will keep trying myself and update the code if I make progress.
SELECT
regio, 1995 as year, sum("0") as "0", sum("1") as "1", sum("2") as "2", sum("3") as "3", sum("4") as "4", sum("5") as "5", sum("6") as "6", sum("7") as "7", sum("8") as "8", sum("9") as "9", sum("10") as "10"
FROM
source
where
year = 1995 OR "year-1" = 1995 OR "year-2" = 1995 OR "year-3" = 1995 OR "year-4" = 1995
group by
regio
UNION
SELECT
regio, 1996 as year, sum("0") as "0", sum("1") as "1", sum("2") as "2", sum("3") as "3", sum("4") as "4", sum("5") as "5", sum("6") as "6", sum("7") as "7", sum("8") as "8", sum("9") as "9", sum("10") as "10"
FROM
source
where
year = 1996 OR "year-1" = 1996 OR "year-2" = 1996 OR "year-3" = 1996 OR "year-4" = 1996
group by
regio

Answer 1

You would seem to want:
SELECT regio, g.yyyy as year, sum("0") as "0", sum("1") as "1",
sum("2") as "2", sum("3") as "3", sum("4") as "4",
sum("5") as "5", sum("6") as "6", sum("7") as "7",
sum("8") as "8", sum("9") as "9", sum("10") as "10"
FROM source CROSS JOIN
generate_series(1995, 2017) g(yyyy)
WHERE g.yyyy IN (year, "year-1", "year-2", "year-3", "year-4")
GROUP BY regio, g.yyyy;