SQL query to select only grandchildren

Question

I\'m pretty new to SQL, trying to wrap my head around it, but it\'s getting a little confusing. Here\'s a simplified version of what I\'m working with.

I have this

Answer 1

This can be solved using a simple JOIN.

To select the list of children:

SELECT c.name
FROM people p
JOIN people c ON c.parent_id = p.id
WHERE p.parent_id = 0

To select the list of grandchildren:

SELECT gc.name
FROM people p
JOIN people c ON c.parent_id = p.id
JOIN people gc ON gc.parent_id = c.id
WHERE p.parent_id = 0