Re: Do Views offer any performance advantage?

Tom Lane wrote:

>
>There is probably some minuscule cost difference involved --- you save
>parsing and parse analysis of a long query string.  On the other hand,
>you pay to pull the view definition from the catalogs and merge it into
>the given query.  I'd not care to hazard a guess on whether the actual
>net cost is more or less; but in any case these costs will be swamped
>by query planning and execution, if the query is complex.
>
Actually, there are cases when a view can impact performance.
If you are joining a view, it seems to be treated as a subquery, that
might have a much larger result than you would like.

Imagine
SELECT something
  FROM A JOIN B JOIN C ...
 WHERE A.primaryKeyFoo=1234 ...

 where C is a view, containing JOINs itself, I observed a query plan
(7.3.2) like
A JOIN B JOIN (D JOIN E)
instead of
A JOIN B JOIN D JOIN E which would be much more efficient for the
A.primaryKeyFoo restriction.