From: | Tony Shelver <tshelver(at)gmail(dot)com> |
---|---|
To: | pgsql-sql(at)lists(dot)postgresql(dot)org |
Subject: | Re: How to generate the order if you know the next item for each item? |
Date: | 2021-08-05 14:33:36 |
Message-ID: | CAG0dhZCWoSGorUqCidfM9P_nz6yzx9W1zYmjt-0j9oo7Hjv8gQ@mail.gmail.com |
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Lists: | pgsql-sql |
We have some ordered processing that we need to do that can involve reading
through 10s of thousands of records, with a lot of conditional processing.
We use functions almost exclusively for this, returning a table of results.
On Tue, 3 Aug 2021 at 18:22, David G. Johnston <david(dot)g(dot)johnston(at)gmail(dot)com>
wrote:
> On Tue, Aug 3, 2021 at 8:40 AM Rockdale Green <rockdale(dot)green(at)gmail(dot)com>
> wrote:
>
>> can I do it in one query?
>>
>
> Yes.
>
>> It might be just very simple and I have tried but somehow I am blocked.
>>
>>
> The feature you need is a recursive CTE (WITH RECURSIVE clause). It
> requires an initial row (which in this case is task 3, the only task that
> doesn't appear as a task_order value) and a query to retrieve the next
> row(s) using the information available in the previous iteration.
>
> The documentation and/or online resources can walk you through the
> specifics.
>
> David J.
>
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