How to use aggregate functions when using recursive query in postgresql - postgresql

Question

On multiple iteration on a recursive query in postgresql, I have got the following result when i run the below query
WITH recursive report AS (
select a.name, a.id, a.parentid, sum(b.id)
from table1 a
INNER JOIN table2 b on a.id=b.table1id
GROUP by a.name, a.id, a.parentid
), report2 AS (
SELECT , 0 as lvl
FROM report
WHERE parentid IS NULL
UNION ALL
SELECT child., parent.lvl + 1
FROM report child
JOIN report2 parent
ON parent.id = child.parentid
)
select * from report2
I want to sum the count column with the top most level, so my output should be like below,
What is the best possible way to get it.

Answer 1

If you calculate a path during recursion, like so:
WITH recursive report AS (
select a.name, a.id, a.parentid, sum(b.id) -- Is summing b.id the right thing here?
from table1 a
INNER JOIN table2 b on a.id=b.table1id
GROUP by a.name, a.id, a.parentid
), report2 AS (
SELECT report.*, 0 as lvl, array[report.id] as path_array
FROM report
WHERE parentid IS NULL
UNION ALL
SELECT child.*, parent.lvl + 1, report2.path_array||report.id
FROM report child
JOIN report2 parent
ON parent.id = child.parentid
)
select * from report2;
Do you really mean sum(b.id) and not count(*) in the report CTE?
You can get the sum of count for your top levels using this query as the main query from your recursion:
select t.name, sum(r.count) as total_count
from report2 r
join table1 t
on t.id = r.path_array[1]
group by t.name;