Waiting for PostgreSQL 14 – SEARCH and CYCLE clauses

On 1st of February 2021, Peter Eisentraut committed patch:

SEARCH and CYCLE clauses 
This adds the SQL standard feature that adds the SEARCH and CYCLE
clauses to recursive queries to be able to do produce breadth- or
depth-first search orders and detect cycles.  These clauses can be
rewritten into queries using existing syntax, and that is what this
patch does in the rewriter.
Reviewed-by: Vik Fearing <vik@postgresfriends.org>
Reviewed-by: Pavel Stehule <pavel.stehule@gmail.com>
Discussion: https://www.postgresql.org/message-id/flat/db80ceee-6f97-9b4a-8ee8-3ba0c58e5be2@2ndquadrant.com

Continue reading Waiting for PostgreSQL 14 – SEARCH and CYCLE clauses

r/trees ( recursive trees, what did you think about? )

I got asked on irc to show some examples how to use recursive CTE. Apparently my previous post wasn't good enough 🙂

I think that most of the users will use recursive cte to deal with trees I decided to show how to use it, even though it's not my favorite approach to dealing with trees in SQL.

Continue reading r/trees ( recursive trees, what did you think about? )

Getting list of all children in “adjacency list” tree structure

So, you have a table which looks like this:

# \d test
                           Table "public.test"
  Column   |  Type   |                     Modifiers
 id        | integer | not null default nextval('test_id_seq'::regclass)
 parent_id | integer |
 x         | text    |
    "test_pkey" PRIMARY KEY, btree (id)
Foreign-key constraints:
    "test_parent_id_fkey" FOREIGN KEY (parent_id) REFERENCES test(id)
Referenced by:
  "test_parent_id_fkey" IN test FOREIGN KEY (parent_id) REFERENCES test(id)

And you would like to easily get all children starting from given node?

Continue reading Getting list of all children in “adjacency list" tree structure

My take on trees in SQL

Quick note in polish: jeśli znasz moje poprzednie posty nt. drzew, to ten możesz sobie pewnie odpuścić. będzie zawierał jedynie opis implementacji zbliżony do tego co już jest dostępne.

OK, back to English (or at least my version of English).

Finding a good way to store trees in SQL was/is my long-term hobby. I tried ltree, basic adjacency list, Celko's nested sets way, and nothing really was able to make me feel satisfied.

Ltree is great, but PostgreSQL only (not that it's a big problem). Adjacency list is very simple in insert, update and delete operations, but forces me to use recursive queries in case of some not-so-standard queries. Nested sets are quite the contrary – great for selects, but I simply hate writing insert/update/delete to these trees.

Is there anything better? I think so.

Continue reading My take on trees in SQL