On 1/4/17, Gwork <nnj@xxxxxxxxxx> wrote: > On 1/5/17 2:22 AM, Vitaly Burovoy wrote: >> On 1/4/17, Vitaly Burovoy <vitaly.burovoy@xxxxxxxxx> wrote: >>> On 1/4/17, Gwork <nnj@xxxxxxxxxx> 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) >> I'm sorry, forgot to mention: If you want to deal with hierarchical >> data, Postgres has better solution - recursive query[1]. When you >> understand principles, it will be much easier for you to write queries >> instead of mentioned in the article. >> >> For example, "Retrieving a Single Path" from "Adjacency model" can be >> written as: >> WITH RECURSIVE >> sel(name, parent, depth) AS ( >> SELECT name, parent, 0 FROM category WHERE name='FLASH' >> UNION ALL >> SELECT c.name, c.parent, depth + 1 FROM category c, sel WHERE >> c.category_id=sel.parent >> ) >> SELECT name FROM sel >> ORDER BY depth DESC; >> >> which gives the same result and not depends on "parent.lft" which >> don't have to increase. >> >> Moreover, you don't need to lock a table when you change data and you >> can even add a constraint to keep consistency: >> ALTER TABLE category ADD FOREIGN KEY (parent) REFERENCES >> category(category_id) ON UPDATE CASCADE ON DELETE RESTRICT; >> >> [1]https://www.postgresql.org/docs/current/static/queries-with.html >> > > Hi Vitaly, > > Your first solution worked great! > > I'll like try your second suggestion, I feel is gonna be a better solution > very important to eliminate lock while updating table. > > I'll keep you posted if I have any further issue relating to the query. > > Thank you for helping out. Feel free to ask, but do not forget to add the mailing list in CC (via "Reply to all"). Other people (new users) also can be interested in ways to solve issues. P.S. Moved from -bugs[2] to -general. [2]https://www.postgresql.org/message-id/flat/7582ea1e-6146-fd8d-b564-c2fe251210b2%40riseup.net -- Best regards, Vitaly Burovoy -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
