On Thu, May 27, 2004 at 06:27:47PM -0700, Sailesh Krishnamurthy wrote: > >>>>> "Alvaro" == Alvaro Herrera <[EMAIL PROTECTED]> 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 ? No, there's no rules optimizer, only the cost-based one you already know of. > 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 ? Sorry, I don't know the optimizer code. You can find a lot of detail in backend/optimizer/README. Probably you want to look at what happens to JOIN_IN nodes, for example, regarding the conversion of a WHERE foo IN (SELECT bar FROM ...) into some kind of join. -- Alvaro Herrera (<alvherre[a]dcc.uchile.cl>) "La espina, desde que nace, ya pincha" (Proverbio africano) ---------------------------(end of broadcast)--------------------------- TIP 8: explain analyze is your friend
