Robert Haas wrote:
Currently, use of window functions always forces sorting, ...
That's not strictly true, actually. No sort is done if the input happens
to be sorted already, as in:
postgres=# CREATE TABLE foo (id integer PRIMARY KEY);
NOTICE: CREATE TABLE / PRIMARY KEY will create implicit index
"foo_pkey" for table "foo"
CREATE TABLE
postgres=# INSERT INTO foo SELECT generate_series(1,100);
INSERT 0 100
postgres=# explain SELECT SUM(id) OVER (ORDER BY id) FROM (SELECT * FROM
foo WHERE id < 100) AS a;
QUERY PLAN
-----------------------------------------------------------------------------
WindowAgg (cost=0.00..70.25 rows=800 width=4)
-> Index Scan using foo_pkey on foo (cost=0.00..58.25 rows=800
width=4)
Index Cond: (id < 100)
(3 rows)
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com
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