Re: Reproducing incorrect order with order by in a subquery - Mailing list pgsql-general

On Tue, Jun 13, 2023 at 6:06 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:

Ruslan Zakirov <ruslan.zakirov@gmail.com> writes:
> I know how to fix the problem and I know that ORDER BY should be in the
> outermost select.

> However, I want to write a test case that shows that the old code is wrong,
> but can not create
> minimal set of tables to reproduce it. With this I'm looking for help.

The ORDER BY in the sub-select will be honored at the output of the
sub-select.  To have a different ordering at the final output, you
need the upper query to do something that would re-order the rows.
Joining the sub-select to something else might make that happen,
or you could apply DISTINCT or some other non-trivial processing
in the upper query.

                        regards, tom lane

Hello Tom,

Thanks for replying. Maybe I'm just wrong in my assumption. A user reports incorrect order in the following query:

SELECT main.*, COUNT(main.id) OVER() AS search_builder_count_all FROM (

  SELECT DISTINCT main.* FROM Tickets main

  LEFT JOIN Groups Groups_2 ON ( Groups_2.Domain = 'RT::Ticket-Role' ) AND ( Groups_2.Instance = main.id )

  JOIN Queues Queues_1 ON ( Queues_1.id = main.Queue )

  LEFT JOIN CachedGroupMembers CachedGroupMembers_3 ON ( CachedGroupMembers_3.Disabled = '0' ) AND ( CachedGroupMembers_3.MemberId IN ('38', '837', ... , '987', '58468') ) AND ( CachedGroupMembers_3.GroupId = Groups_2.id )

WHERE ( ( main.Queue IN ('1', ... , '20') OR ( CachedGroupMembers_3.MemberId IS NOT NULL AND LOWER(Groups_2.Name) IN ('cc', 'requestor') ) OR ( main.Owner = '38' ) ) 

   AND (main.IsMerged IS NULL)

   AND (main.Status != 'deleted')

   AND (main.Type = 'ticket')

   AND (main.Owner = '6' AND ( ( Queues_1.Lifecycle = 'default' AND main.Status IN ('new', 'open', 'stalled') ) OR ( Queues_1.Lifecycle = 'approvals' AND main.Status IN ('new', 'open', 'stalled') ) )

) ORDER BY main.Created DESC ) main LIMIT 50

We have an option in our product that makes this query simpler, no joins in the subquery. The user reports that using this option helps with order.  

This is a too complex query to build a test on. Tried simpler scenarios and failed.