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Re: Likely a dead optimizer related code
> Hi Igor,
> I noticed that during Item_cond::fix_fields() and
> Item_func_between::fix_fields() update these optimizer
> related SELECT_LEX members:
> thd->lex->current_select->cond_count and
> The purpose of these members is to allocate optimizer related buffers
> - update_ref_and_keys() in sql_select.cc and
> - check_func_dependency() in opt_table_elimination,cc
> and it seems they have no any other purposes..
> From my understanding, this is a dead code and the collected values are
> never used:
> - cond_count and_between_count are later always initialized to 0
> before the walk(count_sargable_conds) call in update_ref_and_keys().
And the call to check_func_dependency() is done after this call.
> - moreover, using the values collected during fix_fields() would not be
> correct to allocate optimized related buffers, because the code
> in fix_fields() does not distinguish between different query parts,
> so the items can be just a part of the SELECT list rather than a
> part of WHERE/HAVING/ON.
This would note be a problem as the count was supposed to be an upper bound.
As it's not normal that you have many IF or BETWEEN in the SELECT
part, this was not a problem.
I looked at the patch and it's ok to commit.