Re: Postgresql query HAVING do not work

On 1/4/17, Gwork <nnj(at)riseup(dot)net> wrote:
> Version: Postgresql 9.5
> OS: Debian 8 jessie run on docker
>
> 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 |
> +----------------------+---------+
>
> I don't know if I'm doing anything wrong?
>
> Note: Edit the post query by adding node.lft, sub_tree.depth to the
> GROUP BY.

Hello, Gwork,

HAVING works fine, it is just confusing because of naming. HAVING
works with column names from sources (which is "sub_tree.depth" in
your example), not with names of final columns (because they get
aliases later).

You can check it adding depth to your SELECT part:
SELECT node.name, (COUNT(parent.name) - (sub_tree.depth + 1)) AS depth
,array_agg(depth)
FROM nested_category AS node,
...

and you can see that values there are not bigger than 1.

You must use the same expression in HAVING clause as in SELECT one to
get what you want:
HAVING (COUNT(parent.name) - (sub_tree.depth + 1)) <= 1

but the result will not have "FLASH" because it has "2" even in your example.
+----------------------+-------+
| name | depth |
+----------------------+-------+
| PORTABLE ELECTRONICS | 0 |
| MP3 PLAYERS | 1 |
| CD PLAYERS | 1 |
| 2 WAY RADIOS | 1 |
+----------------------+-------+
(4 rows)

--
Best regards,
Vitaly Burovoy