maria-developers team mailing list archive

[Sergey Petrunia <sergey@xxxxxxxxxxx>]

On Sun, Jan 25, 2015 at 08:54:11PM +0100, Sergei Golubchik wrote:
> Hi, Sergey!
> 
> On Jan 25, Sergey Petrunia wrote:
> > Hi Sergei,
> > 
> > == TL;DR ==
> > I have debugged that LEFT JOIN problem. The fix is not pretty, but
> > correct. I will now push it into the 10.0 tree.
> 
> I've spent few hours in the airport and during the flight debugging it.
> Agree with the fix, but it needs a better comment - the one that
> can be understood without few hours of debugging.
> 
> I suggest:
> 
> -      Do not change the order of testing. Fields may be associated
> -      with a TABLE object without being part of the current row.
> -      For NULL value check to work for these fields, they must
> -      have a valid null_ptr, and this pointer must be checked before
> -      TABLE::null_row.
> -
>        Note that if a table->null_row is set then also all null_bits are
>        set for the row.
> +
> +      In the case of the 'result_field' for GROUP BY, table->null_row might
> +      refer to the *next* row in the table (when the algorithm is: read the
> +      next row, see if any of group column values have changed, send the
> +      result - grouped - row to the client if yes). So, table->null_row might
> +      be wrong, but such a result_field is always nullable (that's defined by
> +      original_field->maybe_null()) and we trust its null bit.
>      */
> 
> If you agree, I'll commit this change (it doesn't have to be in 10.0.16,
> of course).
>

Yes, agree.

BR
 Sergei
-- 
Sergei Petrunia, Software Developer
MariaDB Corporation | Skype: sergefp | Blog: http://s.petrunia.net/blog