Re: Access to postgresql query optimizer output

Thanks for the clarification Craig.

On Mon, Oct 29, 2012 at 8:46 AM, Craig Ringer <ringerc(at)ringerc(dot)id(dot)au> wrote:

> On 10/29/2012 04:07 PM, Seref Arikan wrote:
> > Greetings,
> > I keep seeing statements like "Postgresql optimizer rewrites this query
> > as...." What I'm curious about is, is there a way to obtain SQL form of
> > the re-written queries somewhere in the chain of query evaluation? It
> > does not make a lot sense to generate sql again, but it would help a lot
> > to see the queries in their rewritten form.
>
> I've never seen such a tool, and I'm not sure one is possible, though I
> agree it'd be interesting.
>
> The same SQL can result in many different query plans, and there are
> many different SQL statements that can all result in the same query
> plan. How would you unambiguously show what plan the SQL represented?
>
> It's not so much that Pg's planner "rewrites" one SQL statement to
> another. Usually, it's that two or more different SQL statements
> optimize down to the same query plan.
>
> EXPLAIN and EXPLAIN ANALYZE show the query plans, and I'm not really
> sure you can go backwards from there to SQL in any consistent and
> logical way.
>
> --
> Craig Ringer
>
>