Re: IN joining

Tom Lane wrote:

>Dennis Haney <davh(at)diku(dot)dk> writes:
>
>
>>Consider this example:
>>SELECT * FROM a,b WHERE a.id = b.id AND (a.id) IN (SELECT c.id FROM c)
>>the possible execution trees are {{a,b}, {c}}, {{a,c},{b}} and the code
>>seems to also permit {{b,c},{a}}.
>>
>>
>
>No, it does not --- as you say, that would give wrong answers. That
>case is eliminated by the tests following this comment:
>
> * JOIN_IN technique will work if outerrel includes LHS and
> * innerrel is exactly RHS; conversely JOIN_REVERSE_IN handles
> * RHS/LHS.
> *
> * JOIN_UNIQUE_OUTER will work if outerrel is exactly RHS;
> * conversely JOIN_UNIQUE_INNER will work if innerrel is
> * exactly RHS.
>
>Joining {b,c} to {a} does not meet any of those four allowed cases.
>
>
Exactly my point... So why ever bother creating the {b,c} node which is
legal by the above definition?

--
Dennis
use Inline C => q{void p(char*g){
printf("Just Another %s Hacker\n",g);}};p("Perl");