hierarchical query and counting siblings?

Question

I've looked at several different answers on this site and others, but I'm not having much luck figuring out how to count siblings in a hierarchical query.

I'm using Oracle 10g.

SELECT LEVEL, last_name||', '||first_name AS Manager, count(employee_id)
FROM employees
START WITH manager_id IS NULL
CONNECT BY PRIOR employee_id = manager_id
GROUP BY level

This returns 4 levels, and about 80 employees. I'm wanting to add up the number of siblings under the level 2 instead of listing them all. But, I'm getting stuck trying to figure it out.

Any nudges towards the right way? Thanks!

Answer 1

This will count the number of descendents of each employee at level 1 and 2:

SELECT employee_id, manager_id, full_name, emp_level
    ,(
        SELECT COUNT(*)
        FROM employees
        START WITH employees.manager_id = employees2.employee_id
        CONNECT BY prior employee_id = manager_id
    ) descendents
FROM
(
    SELECT employee_id, manager_id, last_name||', '||first_name full_name, LEVEL emp_level
    FROM employees
    START WITH manager_id IS NULL
    CONNECT BY PRIOR employee_id = manager_id
) employees2
WHERE emp_level <= 2;