Re: [SQL] Using Ltree For Hierarchical Structures
From: Don Parris [mailto:parri...@gmail.com] Sent: Tuesday, February 26, 2013 4:55 PM To: pgsql-sql@postgresql.org Subject: Re: Using Ltree For Hierarchical Structures ... I am unaware of the connect_by module, so will have to look into it. ... Cheers! Don For that look into tablefunc Extension. It also has other useful functions, such as crosstab. Regards, Igor Neyman
Re: [SQL] Using Ltree For Hierarchical Structures
From: Don Parris [mailto:parri...@gmail.com] Sent: Sunday, February 24, 2013 5:21 PM To: pgsql-sql@postgresql.org Subject: Using Ltree For Hierarchical Structures Hi all, With many thanks to Misa and others who helped out with my question about working with hierarchical data, I have now written a blog post on how I implemented the ltree module to solve my problem. http://dcparris.net/2013/02/24/using-ltree-hierarchical-postgresql/ Frankly, if you work with hierarchical data, I'm not sure I could recommend it strongly enough. I should think that even experienced, advanced SQL gurus would appreciate the simplicity ltree offers, when compared to the ugly table designs and recursive queries in order to work with hierarchical structures. I really hope this blog post will help others in the same boat. Regards, Don It's all in the eyes of beholder. IMHO, recursive CTEs are perfect for hierarchical structures, and much cleaner than 2-table design using ltree, that you show in the blog. Regards, Igor Neyman -- Sent via pgsql-sql mailing list (pgsql-sql@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-sql
Re: [SQL] Using Ltree For Hierarchical Structures
Hi Igor, I agree it is all in the eyes of beholder. Would be good if you can show how to achieve the goal (Summing on Top Levels categories in hierarchy) with CTE? For example show all categories in level 2 (x), and sum amounts for each... (Sum takes all amounts from all transactions of its child categories in any bellow levels). I have tested both scenarios - and indexed ltree has given better result - though there is a possibility I haven't pick best approach to solve the problem with CTE... I am just interested in performance - implementation detail is less important... Data: Total number of categories: 1000 (in all levels) No of Categories in top level: 5 No of categories in level 2: 20 Total number of levels: can vary - max in my testing was 8... Transaction rows with amounts: 1 000 000 (though I am not sure what u meant by: 2-table design using ltree, and with CTE there are 2 tables... Categories and Transactions: just in categories instead of ltree datatype, is integer datatype: parent_id) Many thanks, Misa 2013/2/26 Igor Neyman iney...@perceptron.com From: Don Parris [mailto:parri...@gmail.com] Sent: Sunday, February 24, 2013 5:21 PM To: pgsql-sql@postgresql.org Subject: Using Ltree For Hierarchical Structures Hi all, With many thanks to Misa and others who helped out with my question about working with hierarchical data, I have now written a blog post on how I implemented the ltree module to solve my problem. http://dcparris.net/2013/02/24/using-ltree-hierarchical-postgresql/ Frankly, if you work with hierarchical data, I'm not sure I could recommend it strongly enough. I should think that even experienced, advanced SQL gurus would appreciate the simplicity ltree offers, when compared to the ugly table designs and recursive queries in order to work with hierarchical structures. I really hope this blog post will help others in the same boat. Regards, Don It's all in the eyes of beholder. IMHO, recursive CTEs are perfect for hierarchical structures, and much cleaner than 2-table design using ltree, that you show in the blog. Regards, Igor Neyman -- Sent via pgsql-sql mailing list (pgsql-sql@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-sql
Re: [SQL] Using Ltree For Hierarchical Structures
Hi Igor, As Misa points out, my original design used 2 tables - category line-items. Either way it's two tables.The biggest difference lies in the approach to summing line-items by various levels of category - with each branch of the tree having different levels. I cannot speak to performance, but understanding CTEs has been difficult for me. Ltree is so much simpler. I am certain there is a place for CTEs, but why torture myself trying to hash out a CTE when ltree makes the queries so much easier to write? On Feb 26, 2013 11:14 AM, Misa Simic misa.si...@gmail.com wrote: Hi Igor, I agree it is all in the eyes of beholder. Would be good if you can show how to achieve the goal (Summing on Top Levels categories in hierarchy) with CTE? For example show all categories in level 2 (x), and sum amounts for each... (Sum takes all amounts from all transactions of its child categories in any bellow levels). I have tested both scenarios - and indexed ltree has given better result - though there is a possibility I haven't pick best approach to solve the problem with CTE... I am just interested in performance - implementation detail is less important... Data: Total number of categories: 1000 (in all levels) No of Categories in top level: 5 No of categories in level 2: 20 Total number of levels: can vary - max in my testing was 8... Transaction rows with amounts: 1 000 000 (though I am not sure what u meant by: 2-table design using ltree, and with CTE there are 2 tables... Categories and Transactions: just in categories instead of ltree datatype, is integer datatype: parent_id) Many thanks, Misa 2013/2/26 Igor Neyman iney...@perceptron.com From: Don Parris [mailto:parri...@gmail.com] Sent: Sunday, February 24, 2013 5:21 PM To: pgsql-sql@postgresql.org Subject: Using Ltree For Hierarchical Structures Hi all, With many thanks to Misa and others who helped out with my question about working with hierarchical data, I have now written a blog post on how I implemented the ltree module to solve my problem. http://dcparris.net/2013/02/24/using-ltree-hierarchical-postgresql/ Frankly, if you work with hierarchical data, I'm not sure I could recommend it strongly enough. I should think that even experienced, advanced SQL gurus would appreciate the simplicity ltree offers, when compared to the ugly table designs and recursive queries in order to work with hierarchical structures. I really hope this blog post will help others in the same boat. Regards, Don It's all in the eyes of beholder. IMHO, recursive CTEs are perfect for hierarchical structures, and much cleaner than 2-table design using ltree, that you show in the blog. Regards, Igor Neyman -- Sent via pgsql-sql mailing list (pgsql-sql@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-sql
Re: [SQL] Using Ltree For Hierarchical Structures
Don Parris wrote on 24.02.2013 23:20: With many thanks to Misa and others who helped out with my question about working with hierarchical data, I have now written a blog post on how I implemented the ltree module to solve my problem. http://dcparris.net/2013/02/24/using-ltree-hierarchical-postgresql/ Frankly, if you work with hierarchical data, I'm not sure I could recommend it strongly enough. I should think that even experienced, advanced SQL gurus would appreciate the simplicity ltree offers, when compared to the ugly table designs and recursive queries in order to work with hierarchical structures. I really hope this blog post will help others in the same boat. How do you ensure referential integrity with this approach? (i.e. make sure that all elements from the path column actually point to an existing category) Thomas -- Sent via pgsql-sql mailing list (pgsql-sql@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-sql
Re: [SQL] Using Ltree For Hierarchical Structures
From: Don Parris [mailto:parri...@gmail.com] Sent: Tuesday, February 26, 2013 1:23 PM To: Misa Simic Cc: Igor Neyman; pgsql-sql@postgresql.org Subject: Re: [SQL] Using Ltree For Hierarchical Structures Hi Igor, As Misa points out, my original design used 2 tables - category line-items. Either way it's two tables. The biggest difference lies in the approach to summing line-items by various levels of category - with each branch of the tree having different levels. I cannot speak to performance, but understanding CTEs has been difficult for me. Ltree is so much simpler. I am certain there is a place for CTEs, but why torture myself trying to hash out a CTE when ltree makes the queries so much easier to write? Don, To answer this question... Before I worked (mostly) with Oracle which has connect by construct to work with hierarchies. So, when I switched to Postgres I was happy to find connect_by contrib. modul. And with more recent PG versions, it was just natural transition from contrib. module to recursive CTEs. Igor -- Sent via pgsql-sql mailing list (pgsql-sql@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-sql
Re: [SQL] Using Ltree For Hierarchical Structures
On Tue, Feb 26, 2013 at 2:30 PM, Igor Neyman iney...@perceptron.com wrote: From: Don Parris [mailto:parri...@gmail.com] Sent: Tuesday, February 26, 2013 1:23 PM To: Misa Simic Cc: Igor Neyman; pgsql-sql@postgresql.org Subject: Re: [SQL] Using Ltree For Hierarchical Structures Hi Igor, As Misa points out, my original design used 2 tables - category line-items. Either way it's two tables.The biggest difference lies in the approach to summing line-items by various levels of category - with each branch of the tree having different levels. I cannot speak to performance, but understanding CTEs has been difficult for me. Ltree is so much simpler. I am certain there is a place for CTEs, but why torture myself trying to hash out a CTE when ltree makes the queries so much easier to write? Don, To answer this question... Before I worked (mostly) with Oracle which has connect by construct to work with hierarchies. So, when I switched to Postgres I was happy to find connect_by contrib. modul. And with more recent PG versions, it was just natural transition from contrib. module to recursive CTEs. Igor That is helpful to know. I am unaware of the connect_by module, so will have to look into it. It is good to know about Oracle's Connect By construct - I wondered how they dealt with that. If nothing else, I am learning more about CTE's. This whole thread came about because, while I am normally able to look at example code and translate that into my particular problem, I really got myself in over my head with this category tree. Most of my queries have been fairly simple so far, but this one stumped me due to my lack of experience. In the meanwhile, I think understanding CTEs is probably still an important skill, so I am sure I should be familiar with both. I greatly appreciate everyone's contributions - I am learning a great deal here. It's one of the reasons why I post my blog stories - to give back a little something of what I've discovered and learned. Misa gave me an example of CTE code to play around with, and I am going to tackle that in more depth later this week. Cheers! Don -- D.C. Parris, FMP, Linux+, ESL Certificate Minister, Security/FM Coordinator, Free Software Advocate http://dcparris.net/ https://www.xing.com/profile/Don_Parrishttp://www.linkedin.com/in/dcparris GPG Key ID: F5E179BE
Re: [SQL] Using Ltree For Hierarchical Structures
2013/2/26 Thomas Kellerer spam_ea...@gmx.net Don Parris wrote on 24.02.2013 23:20: With many thanks to Misa and others who helped out with my question about working with hierarchical data, I have now written a blog post on how I implemented the ltree module to solve my problem. http://dcparris.net/2013/02/**24/using-ltree-hierarchical-**postgresql/http://dcparris.net/2013/02/24/using-ltree-hierarchical-postgresql/ Frankly, if you work with hierarchical data, I'm not sure I could recommend it strongly enough. I should think that even experienced, advanced SQL gurus would appreciate the simplicity ltree offers, when compared to the ugly table designs and recursive queries in order to work with hierarchical structures. I really hope this blog post will help others in the same boat. How do you ensure referential integrity with this approach? (i.e. make sure that all elements from the path column actually point to an existing category) Thomas Hi Thomas, Yes we met that problem and it further makes deeper problems... i.e. what if some category in up level - change his parent (updated path field) - path must be changed for all childs... Of several solutions - we have picked to use the best from both worlds... So we still use - parent_id column... and ltree is used just as materialized path - to improve performance... I think Materialized Views what comming in 9.3 - (I still havent seen how it works) - will help in that way - we will see...
