From: Roy Lyseng
Date: December 16 2010 11:01pm
Subject: Re: bzr commit into mysql-5.1 branch (ole.john.aske:3477) Bug#58490
List-Archive: http://lists.mysql.com/commits/127120
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Hi Guilhem,

about this section:

> If I don't forget, I will later do a change which will save a useless test: we
> have this code in evaluate_join_record():
>
> bool select_cond_result= TRUE;
>
> if (error > 0 || (join->thd->is_error())) // Fatal error
> return NESTED_LOOP_ERROR;
> if (error < 0)
> return NESTED_LOOP_NO_MORE_ROWS;
> if (join->thd->killed) // Aborted by user
> {
> join->thd->send_kill_message();
> return NESTED_LOOP_KILLED; /* purecov: inspected */
> }
> DBUG_PRINT("info", ("select cond 0x%lx", (ulong)select_cond));
>
> if (select_cond)
> {
> select_cond_result= test(select_cond->val_int());
>
> /* check for errors evaluating the condition */
> if (join->thd->is_error())
> return NESTED_LOOP_ERROR;
> }
>
> if (!select_cond || select_cond_result)
> {
> ...
>
> I claim that the test above:
> if (!select_cond || select_cond_result)
> can be replaced with
> if (select_cond_result)
> because:
> a) if (select_cond_result) is true then (!select_cond || select_cond_result) is
> true too
> b) if (!select_cond || select_cond_result) is true, then either:
> b1) (select_cond_result) is true, or
> b2) (!select_cond) is true, which means that the if(select_cond) was not
> entered, so select_cond_result is still at its initial value, which is TRUE.

In 5.6, I simplified this section by replacing "select_cond_result" with the 
more general "found" variable. IMHO, there is no need to elaborate the solution 
for 5.1/5.5.

Thanks,
Roy