SQL - Group values by range - sql

Question

I have following query:
SELECT
polutionmm2 AS metric,
sum(cnt) as value
FROM polutiondistributionstatistic as p inner join crates as c on p.crateid = c.id
WHERE
c.name = '154'
and to_timestamp(startts) >= '2021/01/20 00:00:00' group by polutionmm2
this query returns these values:
"metric","value"
50,580
100,8262
150,1548
200,6358
250,869
300,3780
350,505
400,2248
450,318
500,1674
550,312
600,7420
650,1304
700,2445
750,486
800,985
850,139
900,661
950,99
1000,550
I would need to edit the query in a way that it groups them toghether in ranges of 100, starting from 0. So everything that has a metric value between 0 and 99 should be one row, and the value the sum of the rows... like this:
"metric","value"
0,580
100,9810
200,7227
300,4285
400,2556
500,1986
600,8724
700,2931
800,1124
900,760
1000,550
The query will run over about 500.000 rows.. Can this be done via query? Is it efficient?
EDIT:
there can be up to 500 ranges, so an automatic way of grouping them would be great.

Answer 1

You can use generate_series() and a range type to generate the the ranges you want, e.g.:
select int4range(x.start, case when x.start = 1000 then null else x.start + 100 end, '[)') as range
from generate_series(0,1000,100) as x(start)
This generates the ranges [0,100), [100,200) and so on up until [1000,).
You can adjust the width and the number of ranges by using different parameters for generate_series() and adjusting the expression that evaluates the last range
This can be used in an outer join to aggregate the values per range:
with ranges as (
select int4range(x.start, case when x.start = 1000 then null else x.start + 100 end, '[)') as range
from generate_series(0,1000,100) as x(start)
)
select r.range as metric,
sum(t.value)
from ranges r
left join the_table t on r.range #> t.metric
group by range;
The expression r.range #> t.metric tests if the metric value falls into the (generated) range
Online example

Answer 2

You can create a Pseudo table with interval you like and join with that table.
I'll use recursive CTE for this case.
WITH RECURSIVE cte AS(
select 0 St, 99 Ed
UNION ALL
select St + 100, Ed + 100 from cte where St <= 1000
)
select cte.st as metric,sum(tb.value) as value from cte
inner join [tableName] tb --with OP query result
on tb.metric between cte.St and cte.Ed
group by cte.st
order by st
here is DB<>fiddle with some pseudo data.

Answer 3

use conditional aggregation
SELECT
case when polutionmm2>=0 and polutionmm2<100 then '100'
when polutionmm2>=100 and polutionmm2<200 then '200'
........
when polutionmm2>=900 and polutionmm2<1000 then '1000'
end AS metric,
sum(cnt) as value
FROM polutiondistributionstatistic as p inner join crates as c on p.crateid = c.id
WHERE
c.name = '154'
and to_timestamp(startts) >= '2021/01/20 00:00:00'
group by case when polutionmm2>=0 and polutionmm2<100 then '100'
when polutionmm2>=100 and polutionmm2<200 then '200'
........
when polutionmm2>=900 and polutionmm2<1000 then '1000'
end