Re: Disable cross products in postgres

But then is there some way to tell Optimizer not to consider transitive
joins ?

Or to know if the join is transitive or not ?
On 14-Oct-2017 3:43 AM, "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> Gourav Kumar <gourav1905(at)gmail(dot)com> writes:
> > For e.g. I am checking for this query
> > ...
> > where
> > and ss1.ca_county = ss2.ca_county
> > and ss2.ca_county = ss3.ca_county
> > and ss1.ca_county = ws1.ca_county
> > and ws1.ca_county = ws2.ca_county
> > and ws1.ca_county = ws3.ca_county
>
> > It doesn't has a join predicate between ss1 and ws2 or ss1 and ws3. But
> > optimizer still considers a join among them.
>
> Sure it does, after transitive propagation of those equalities;
> for instance we can derive ss1.ca_county = ws2.ca_county from
> the above-quoted conditions. And it would be very stupid of the
> optimizer not to consider those derived join conditions, because
> they may lead to the optimal join order.
>
> In general it's already true that the optimizer doesn't consider
> clauseless joins unless there's no other choice. But this example
> isn't showing such a case.
>
> regards, tom lane
>