Głębokość w MYSQL i drzewa tabeli zamykania

Dodaj głębokość+1 do pierwszego SELECT.

INSERT INTO closure_tree_path (ancestor, descendant, depth)
SELECT ancestor, '{$node_id}', depth+1 FROM closure_tree_path
WHERE descendant = '{$parent_id}'
UNION ALL SELECT '{$node_id}', '{$node_id}', 0;