Re: How to generate the order if you know the next item for each item?

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.g.johnston@gmail.com> wrote:

On Tue, Aug 3, 2021 at 8:40 AM Rockdale Green <rockdale.green@gmail.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.