Recursive SQL query to find all nodes in a tree beyond a certain depth. This is for PostgreSQL specifically; however, other RDBMS that support recursive CTEs (e.g. Oracle, SQL Server) should be able to do this as well with a slight modification to the syntax.

tree_depth.sql

with recursive base as (
    select * from categories_category
), tree as (
    select id, parent_id, 1 as level, name :: text
    from base as root
    where parent_id is null
    union all
    select child.id, child.parent_id, parent.level + 1, (parent.name || ' > ' || child.name) :: text
    from tree as parent
    join base as child
        on (parent.id = child.parent_id)
)
select name
from tree
where level > 4;