Depth in MYSQL and Closure Table Trees

Question

How would I go about populating a closure table\'s depth/length column when inserting a new node to the tree?

The values in ancestor and descendant are IDs from another

Answer 1

Add depth+1 to the first 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;