Re: Propogating conditions into a query

Tom Lane wrote:
> Phil Endecott <spam_from_postgresql_general@chezphil.org> writes:
>
>>I have a number of complex views for which the typical use is to select
>>exactly one row by id, e.g.  "select * from V where id=nnn".  Some of
>>these selects run orders of magnitude faster than others.  Looking at
>>the output of "explain analyse" it seems that in the fast cases the
>>"id=nnn" condition is passed down to the lower-level operations, while
>>in the slower cases the entire view is created and then filtered using
>>the condition as a final step.
>
> When in doubt, use the source ;-) ... most sorts of things like this are
> pretty well commented, if you can find the relevant code.

Good plan.

>  * 3. If the subquery uses DISTINCT ON, we must not push down any quals that
>  * refer to non-DISTINCT output columns, because that could change the set
>  * of rows returned.

OK, so this is why my query with DISTINCT ON was failing.  I can fix that.

I don't see anything in there about LEFT OUTER JOIN though.  Any ideas?

--Phil.