How to write a CTE to aggregate hierarchical values - sql

Question

I want to write expressions in sqlite to process a tree of items, starting with the leaf nodes (the bottom) and proceeding back to their parents all the way to the root node (the top), such that each parent node is updated based on the content of its children. I've been able to write a CTE that does something similar, but isn't yet totally correct.
I have a simple table "test1" containing some nested values:
id | parent | value | total
---+--------+--------------
1 | NULL | NULL | NULL
2 | 1 | NULL | NULL
3 | 2 | NULL | NULL
4 | 3 | 50 | NULL
5 | 3 | 50 | NULL
6 | 2 | 60 | NULL
7 | 6 | 90 | NULL
8 | 6 | 60 | NULL
Rows may have children who reference their parent via their parent field. Rows may have a value of their own as well as child rows, or they may simply be parents without values (ie. "wrappers"). The leafs would be the rows without any children.
For each row I'd like to calculate the total, as the average or the row's value (if not null) AND its children's totals. This should start with the leaf nodes and proceed up the tree to their parents, all the way to the root node at the top of the data hierarchy.
I've tried a number of variations of CTE's but am having difficulty writing one that will recursively calculate these totals from the bottom up.
Currently, I have:
UPDATE test1 SET total = (
WITH RECURSIVE cte(cte_id,cte_parent,cte_value,cte_total) AS (
SELECT test1.id, test1.parent, test1.value, test1.total
UNION ALL
select t.id, t.parent, t.value, t.total from test1 t, cte
WHERE cte.cte_id=t.parent
) SELECT AVG(cte_value) FROM cte
);
which produces:
id | parent | value | total
---+--------+-------+------
1 | NULL | NULL | 62
2 | 1 | NULL | 62
3 | 2 | NULL | 50
4 | 3 | 50 | 50
5 | 3 | 50 | 50
6 | 2 | 60 | 70
7 | 6 | 90 | 90
8 | 6 | 60 | 60
Looking at the top-most rows, this is not quite right, since it's taking an average of not only the row's immediate children, but of all the row's descendants. This causes row 2 for example to have a total of 62 instead of 60. The expected results should set rows 2's total to 60, as the average of its immediate child rows 3 and 6. Row 1's total would be 60 as well.
How can I calculate a "total" value for each row based on an average of the row's value and the values of it's immediate children only, while ensuring the upper levels of the hierarchy are correctly populated based on the calculated totals of their children?

Answer 1

It turns out that a very similar question and solution was posted here:
How can I traverse a tree bottom-up to calculate a (weighted) average of node values in PostgreSQL?
Since sqlite3 doesn't let you create functions, the example using a recursive CTE applies:
with recursive cte(id, parent, value, level, total) as (
select
t.id, t.parent, t.value,
0,
t.value as total
from test1 t
where not exists (
select id
from test1
where parent = t.id)
union all
select
t.id, t.parent, t.value,
c.level+1,
case when t.value is null then c.total else t.value end
from test1 t
join cte c on t.id=c.parent
)
select id, parent, value, avg(total) total from (
select
id, parent, value, level, avg(total) total
from cte
group by id,parent,level
)
group by id, parent
order by id