maria-developers team mailing list archive

[Oleg Smirnov <oleg.smirnov@xxxxxxxxxxx>]

Talking about input: I generally don't like code blocks like that:

while (auto next_field= it++)

'cause
-  it's easy to overlook the iterator increment
- you must remember that you cannot use iterator inside the loop since it's
already shifted to next element
- if you break the loop you must again remember that the iterator points to
the next element and not the last one that was processed.

But anyway this is a small detail, I've applied the patch.

On Sun, Jun 12, 2022 at 7:18 PM Sergey Petrunia <sergey@xxxxxxxxxxx> wrote:

> Hi Oleg,
>
> Please fix compile errors on this platform:
> https://buildbot.mariadb.org/#/builders/146/builds/13126/steps/5/logs/stdio
>
> also please apply the attached diff that fixes the coding style and wording
> of comments (input and/or adjustments are welcome).
>
> After this, the patch is ok to push.
>
> The next steps are to create a branch with name like
> preview-10.10-mdev26278-table-elimination and to officially submit it for
> preview tree build and testing.
>
> > commit 7275bf4939248959b5017314d6b0393296831c0c (HEAD,
> origin/bb-10.9-MDEV-26278-look)
> > Author: Oleg Smirnov <olernov@xxxxxxxxx>
> > Date:   Thu Feb 17 22:53:37 2022 +0700
> >
> >     MDEV-26278 Add functionality to eliminate derived tables from the
> query
> >
> >     Elimination of unnecessary tables from SQL queries is already present
> >     in MariaDB. But it only works for regular tables and not for derived
> ones.
> >
> >     Imagine we have a view:
> >       CREATE VIEW v1 AS SELECT a, b, max(c) AS maxc FROM t1 GROUP BY a, b
> >
> >     Due to "GROUP BY a, b" the values of combinations {a, b} are unique,
> >     and this fact can be treated as like derived table "v1" has a unique
> key
> >     on fields {a, b}.
> >
> >     Suppose we have a SQL query:
> >       SELECT t2.* FROM t2 LEFT JOIN v1 ON t2.a=v1.a and t2.b=v1.b
> >
> >     1. Since {v1.a, v1.b} is unique and both these fields are bound to
> t2,
> >        "v1" is functionally dependent on t2.
> >        This means every record of "t2" will be either joined with
> >        a single record of "v1" or NULL-complemented.
> >     2. No fields of "v1" are present on the SELECT list
> >
> >     These two facts allow the server to completely exclude (eliminate)
> >     the derived table "v1" from the query.
>
> BR
>  Sergei
> --
> Sergei Petrunia, Software Developer
> MariaDB Corporation | Skype: sergefp | Blog: http://petrunia.net
>
>
>

-- 
Best regards,
-------------------------
*Oleg Smirnov*
Sr. Software Engineer
MariaDB Server Team