Re: On query rewrite

>>>>> "Alvaro" == Alvaro Herrera <alvherre(at)dcc(dot)uchile(dot)cl> writes:

>> For instance, in the presence of a view or a subquery, does PG
>> do a subquery to join transformation ?

Alvaro> Yes, there are transformations of this sort, but they are
Alvaro> not called query rewrite in the code's terminology, but
Alvaro> "optimization" -- rewrite (rules and views) happens to the
Alvaro> parsed statement, and the optimizer works on the output of
Alvaro> rewriting. So actually the optimizations happen whether
Alvaro> there were or not rules or views.

Interesting .. so these are rule-based then ? Not cost-based ?

I understand that there is a cost-based optimizer anyway that does the
planning and selects the right plan .. but does this come _after_ all
these transformations ? Or does it happen along with the
transformations ?

Alvaro> The query's path is SQL -> parse -> rewrite -> optimize ->
Alvaro> execute

Can you please point me to the code that indeed does such
transformations ?

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