Question

I’ve been using the crap out of the Nested Set Model lately. I have enjoyed designing queries for just about every useful operation and view. One thing I’m stuck on is how to select the immediate children (and only the children, not further descendants!) of a node.

To be honest, I do know of a way – but it involves unmanageable amounts of SQL. I’m sure there is a more straightforward solution.

Answer 1

Did you read the article you posted? It’s under the heading ‘Find the Immediate Subordinates of a Node’

SELECT node.name, (COUNT(parent.name) - (sub_tree.depth + 1)) AS depth FROM nested_category AS node,     nested_category AS parent,     nested_category AS sub_parent,     (         SELECT node.name, (COUNT(parent.name) - 1) AS depth         FROM nested_category AS node,         nested_category AS parent         WHERE node.lft BETWEEN parent.lft AND parent.rgt         AND node.name = 'PORTABLE ELECTRONICS'         GROUP BY node.name         ORDER BY node.lft     )AS sub_tree WHERE node.lft BETWEEN parent.lft AND parent.rgt     AND node.lft BETWEEN sub_parent.lft AND sub_parent.rgt     AND sub_parent.name = sub_tree.name GROUP BY node.name HAVING depth <= 1 ORDER BY node.lft; 

However, what I do (this is cheating) is I combined the nested set with adjacency lists — I embed a ‘parent_id’ in the table, so I can easily ask for the children of a node.