Hi Chris,
You don't need to make a a full view - to join it later to "less rows number table")
If you have, function what takes fkey1 as input parameter and returns SET OF (type of your values_view)
i.e.
CREATE OR REPLACE FUNCTION get_filtered_values_view(in_fkey1 integer)
RETURNS SETOF values_view AS
$BODY$select fkey1, fkey3,
(derived1 / max(derived1) over (partition by fkey1)) as derived1,
(derived2 / sum(derived1) over (partition by fkey1)) as derived2
FROM
(
select fkey1, fkey3,
cast(sum((case when (value > 0.0) then 4 else 1 end)) as double precision) as derived1,
sum((case when (value > 0.0) then (value * 4) else (value + 1) end)) as derived2
from values
group by fkey1, fkey3
having fkey1 = $1
) t$BODY$
LANGUAGE sql STABLE
COST 100
ROWS 1000;
ALTER FUNCTION get_filtered_values_view(integer)
OWNER TO postgres;
Then you can make new function what takes values from table you would like join to view:
CREATE OR REPLACE FUNCTION get_filtered_values_view_joined()
RETURNS SETOF values_view AS
$BODY$
SELECT get_filtered_values_view(
fkey1
)
FROM
(SELECT DISTINCT fkey1 FROM smaller_table_for_join) t
$BODY$
LANGUAGE sql STABLE
COST 100
ROWS 1000;
ALTER FUNCTION get_filtered_values_joined()
OWNER TO postgres;
then you can encapsulate it to final view:
CREATE VIEW final_derived_view AS
SELECT * FROM get_filtered_values_joined()
2013/3/1 Chris Hanks <christopher.m.hanks@xxxxxxxxx>
On Fri, Mar 1, 2013 at 1:21 AM, Raymond O'Donnell <rod@xxxxxx> wrote:
On 01/03/2013 00:19, Chris Hanks wrote:
> On Thu, Feb 28, 2013 at 6:00 AM, Tom Lane <tgl@xxxxxxxxxxxxx
Off the top of my head, I'd imagine it's as simple as:> <mailto:christopher.m.hanks@xxxxxxxxx>> writes:
> > create or replace view values_view as
> > select fkey1, fkey3,
> > (derived1 / max(derived1) over (partition by fkey1)) as derived1,
> > (derived2 / sum(derived1) over (partition by fkey1)) as derived2
> > from (
> > select fkey1, fkey3,
> > cast(sum((case when (value > 0.0) then 4 else 1 end)) as double
> > precision) as derived1,
> > sum((case when (value > 0.0) then (value * 4) else (value + 1)
> end)) as
> > derived2
> > from values
> > group by fkey1, fkey3
> > ) as t1;
>
> > -- This query requires a sequential scan on values, though all the
> data it
> > needs could be found much more efficiently with an index scan.
> > explain analyze select * from values_view where fkey1 = 1263;
>
> To use the outer WHERE clause as an index constraint, postgres would
> have to prove that scanning only the rows with fkey1 = 1263 would still
> find all the rows that would get examined by the window functions ---
> and in this case, it's not only the window functions that make that less
> than obvious, but the grouped aggregates in the sub-select below them.
> There's not nearly that amount of intelligence in the system about
> window functions, as yet. So you'll have to write out the query
> longhand and put the WHERE clause at the lower level, if you want this
> optimization to happen.
>
> regards, tom lane
>
>
> Ok, that makes sense, thanks.
>
> Can anyone point me to an example of wrapping a function in a view, like
> Merlin suggested? I'm not sure how that would work.
create view ... as
select * from my_function(...);
:-)
Ray.
--
Raymond O'Donnell :: Galway :: Ireland
rod@xxxxxx
Sorry, I don't understand. I'm able to make a function that takes an integer and uses it in the subselect as "WHERE fkey1 = arg", and that works as I expect it to and it's plenty fast. But I don't see how to write a view to take advantage of this function - what arguments would go in my_function(...) when I'm declaring the view?Chris
