Re: Default ordering option - Mailing list pgsql-general

From Cyril Champier
Subject Re: Default ordering option
Date
Msg-id CAJaA8VfVBQ1X+ggm5zO7BUFcvXvY0t+8_M+Ei94t=xKFCLHwow@mail.gmail.com
Whole thread Raw
In response to Re: Default ordering option  (Peter Eisentraut <peter.eisentraut@2ndquadrant.com>)
Responses Re: Default ordering option
Re: Default ordering option
List pgsql-general
Adrian:
If order is not an issue in the production code why test for it in the 
test code?

In many cases, it would not be a problem in tests if we had an unordered array comparison helper.
But in other cases, it is a production issue.
In ruby ActiveRecord for exemple, you can do `Patient.find_by(last_name: 'champier')`,
which translates to `SELECT  "patients".* FROM "patients" WHERE "patients"."last_name" = 'champier' LIMIT 1`.
If last_name is not unique, the returned record will be random.

So yes, everything as to be randomized, because the sources are multiples and the consequences can vary to a dramatic production bug, a failed CI 1% of the time, or to a useless test assertion.


Peter:
It might be an interesting exercise to implement this as a post-parsing
hook.
 
I known nothing about that, but that sounds interesting, do you have any documentation pointer to help me implement that?



On Wed, Jul 24, 2019 at 10:36 PM Peter Eisentraut <peter.eisentraut@2ndquadrant.com> wrote:
On 2019-07-23 17:43, Cyril Champier wrote:
> In this documentation
> <https://www.postgresql.org/docs/9.1/queries-order.html>, it is said:
>
>     If sorting is not chosen, the rows will be returned in an
>     unspecified order. The actual order in that case will depend on the
>     scan and join plan types and the order on disk, but it must not be
>     relied on.
>
>
> I would like to know if there is any way to change that to have a "real"
> random behaviour.

It might be an interesting exercise to implement this as a post-parsing
hook.

--
Peter Eisentraut              http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

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