Is it possible to make a recursive SQL query?

Here is an example script using common table expression:

with recursive sumthis(id, val) as (
    select id, value
    from example
    where id = :selectedid
    union all
    select C.id, C.value
    from sumthis P
    inner join example C on P.id = C.parentid
)
select sum(val) from sumthis

The script above creates a ‘virtual’ table called sumthis that has columns id and val. It is defined as the result of two selects merged with union all.

First select gets the root (where id = :selectedid).

Second select follows the children of the previous results iteratively until there is nothing to return.

The end result can then be processed like a normal table. In this case the val column is summed.