The following documentation comment has been logged on the website:
Page: https://www.postgresql.org/docs/9.5/static/tutorial-agg.html
Description:
Following this tutorial The Nested Set Model on
http://mikehillyer.com/articles/managing-hierarchical-data-in-mysql/
Section: Depth of a Sub-Tree.
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, node.lft
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, node.lft, sub_tree.depth
ORDER BY node.lft;
+----------------------+---------+
| name | depth |
|----------------------+---------|
| PORTABLE ELECTRONICS | 0 |
| MP3 PLAYERS | 1 |
| FLASH | 2 |
| CD PLAYERS | 1 |
| 2 WAY RADIOS | 1 |
+----------------------+---------+
Section: 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, node.lft
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, node.lft, sub_tree.depth
HAVING depth <= 1
ORDER BY node.lft;
Adding 'HAVING depth <= 1' to the query still return the same results as
above instead of this:
+----------------------+---------+
| name | depth |
|----------------------+---------|
| PORTABLE ELECTRONICS | 0 |
| MP3 PLAYERS | 1 |
| FLASH | 1 |
| CD PLAYERS | 1 |
| 2 WAY RADIOS | 1 |
+----------------------+---------+
NOTE: I edited the query by add node.lft, sub_tree.depth to the GROUP BY.
I don't know if I'm doing anything wrong?
