mdev-6768-commit-message.mail

> commit a49d2e4bc62507496b85c3499a423b5b4e321354
> Author: Monty <monty@mariadb.org>
> Date:   Fri Mar 31 19:35:04 2023 +0300
>
>     MDEV-6768 Wrong result with aggregate with join with no result set
>     
>     What happens is that end_send_group() is called with a const row but
>     without any rows matching the WHERE clause.
>     This last part is shown by 'join->first_record' not being set.
>     
>     This causes item->no_rows_in_result() to be called for all items to reset
>     all sum functions to their initial state.

The above doesn't describe what the bug was about, does it?

The problem was as follows: 
When a query does implicit grouping and join operation produces an empty 
result set, a NULL-complemented row combination is generated. 
However, constant table fields still show non-NULL values.

Fix the code to produce NULL-complemented records for constant tables as well.
(And also, reset the constant table's records back in case we're in a subquery
which may get re-executed).

>     
>     There is some other issues with the code:
>     - Item_field::no_rows_in_result_set() does not do anything, which causes
>       the fields in constants rows read from tables to be returned in the
>       result set.

It is called no_rows_in_result(). And we do not consider this to be a problem...

>     - join->no_rows_in_result_called is used but never set.
>     - Tables that are used with group functions are not properly marked as
>       maybe_null, which is required if the table rows should be regarded as
>       null-complemented (not existing).
>     - The code that tries to detect if mixed_implicit_grouping should be set
>       didn't take into account all usage of fields and sum functions.
>     - Item_func::restore_to_before_no_rows_in_result() called the wrong
>       function.
>     - join->clear() does not use a table_map argument to clear_tables()
>       which caused it to ignore constant tables.
>     - join->unclear() does not correctly restore status to what is
>       was before join->clear()

There is/was no join->unclear(). You've meant unclear_tables()?
     
>     Fixed by always use a table_map argument to clear_tables() and always use
>     join->clear() and join->unclear() together.

same as above, no join->unclear(). unclear_tables() ? 

>     
>     Other bug fixes:

"More comments" and "Changed return_zero_rows() are technically not "bug fixes".
Please change "bug fixes" to "fixes".

>     - Fixed Item_func::restore_to_before_no_rows_in_result()
>     - Set 'join->no_rows_in_result_called' when no_rows_in_result_set()
>       is called.
>     - Removed not used argument from setup_end_select_func().
>     - More comments
>     - Ensure that end_send_group() modifies the same fields as are in the
>       result set.
>     - Changed return_zero_rows() to use pointers instead of references,
>       similar to the rest of the code.
>
>