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@gmail.com>
> 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