Re: Reproducing incorrect order with order by in a subquery

On Tue, Jun 13, 2023 at 10:55 AM Ruslan Zakirov <ruslan(dot)zakirov(at)gmail(dot)com>
wrote:

> 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.
>
>
If you want guaranteed ordered output you must place the order by in the
outermost query level (i.e., before your limit 50). Trying to do that for
dynamic SQL where you don't actually know what query you are working with
is going to be a challenge - maybe force the user to have the order by
column first in their query then just say "ORDER BY 1" in the wrapper query
you are adding? Basically have them write "row_number() over (order by)"
for their query and you then order by row number.

David J.