Parameters for views based on other views

Hi,
I have a complex query that I want to make more manageable
by splitting it into two separate views and using a third
view to bring the two together. So I have something like
CREATE VIEW vw1 AS
SELECT A.Field1, B.Field2 FROM A, B WHERE A.Field3=B.Field3;

CREATE VIEW vw2 AS
SELECT B.Field5, C.Field6 FROM B, C WHERE B.Field7=C.Field7;

CREATE VIEW vw3 AS
SELECT * FROM vw1, vw2 WHERE vw1.Field1=vw2.Field5;
(the real case for the above is of course much more complicated)

I can now open the third view by
SELECT * FROM vw3 WHERE Field1=13 AND Field2=23;

However this query runs very slow. I tried defining the views with
parameters in the WHERE clauses in each view and I got a MUCH BETTER
performance. So my questions are:
* Why does this happen? Doesn't PG use the parameters to open each view?
* How can I define views with variables as parameters so that I can
assign values to the parameters and then open the view? If there
is a way for this, does it improve performance?
* I am thinking of writing a function that will drop these views and
recreate them with parameters in each view and return the result
of the select statement above. Is this a good idea?
* What is the general way of using complicated parameterized queries
in PG?

Thanks a lot for any suggestions

Nicolas

_________________________________________________________________
Surf the Web without missing calls! Get MSN Broadband.
http://resourcecenter.msn.com/access/plans/freeactivation.asp