The rows considered by a window function are those of the “virtual table” produced by the query’s FROM clause as filtered by its WHERE,GROUP BY,and HAVING clauses if any. For example,a row removed because it does not meet the WHERE condition is not seen by any window function. A query can contain multiple window functions that slice up the data in different ways by means of different OVER clauses,but they all act on the same collection of rows defined by this virtual table.
但是,我没有看到这个.在我看来,像“选择过滤器”非常接近左边距和顶部(最后一件事情).
=# EXPLAIN SELECT * FROM chrome_nvd.view_options where fkey_style = 303451;
QUERY PLAN
----------------------------------------------------------------------------------------------------------------------
Subquery Scan view_options (cost=2098450.26..2142926.28 rows=14825 width=180)
Filter: (view_options.fkey_style = 303451)
-> Sort (cost=2098450.26..2105862.93 rows=2965068 width=189)
Sort Key: o.sequence
-> WindowAgg (cost=1446776.02..1506077.38 rows=2965068 width=189)
-> Sort (cost=1446776.02..1454188.69 rows=2965068 width=189)
Sort Key: h.name,k.name
-> WindowAgg (cost=802514.45..854403.14 rows=2965068 width=189)
-> Sort (cost=802514.45..809927.12 rows=2965068 width=189)
Sort Key: h.name
-> Hash Join (cost=18.52..210141.57 rows=2965068 width=189)
Hash Cond: (o.fkey_opt_header = h.id)
-> Hash Join (cost=3.72..169357.09 rows=2965068 width=166)
Hash Cond: (o.fkey_opt_kind = k.id)
-> Seq Scan on options o (cost=0.00..128583.68 rows=2965068 width=156)
-> Hash (cost=2.21..2.21 rows=121 width=18)
-> Seq Scan on opt_kind k (cost=0.00..2.21 rows=121 width=18)
-> Hash (cost=8.80..8.80 rows=480 width=31)
-> Seq Scan on opt_header h (cost=0.00..8.80 rows=480 width=31)
(19 rows)
这两个WindowAgg本质上将计划改变成似乎从不会更快地完成的任务
QUERY PLAN -------------------------------------------------------------------------------------------------------------------------------------------------------- Subquery Scan view_options (cost=329.47..330.42 rows=76 width=164) (actual time=20.263..20.403 rows=42 loops=1) -> Sort (cost=329.47..329.66 rows=76 width=189) (actual time=20.258..20.300 rows=42 loops=1) Sort Key: o.sequence Sort Method: quicksort Memory: 35kB -> Hash Join (cost=18.52..327.10 rows=76 width=189) (actual time=19.427..19.961 rows=42 loops=1) Hash Cond: (o.fkey_opt_header = h.id) -> Hash Join (cost=3.72..311.25 rows=76 width=166) (actual time=17.679..18.085 rows=42 loops=1) Hash Cond: (o.fkey_opt_kind = k.id) -> Index Scan using options_pkey on options o (cost=0.00..306.48 rows=76 width=156) (actual time=17.152..17.410 rows=42 loops=1) Index Cond: (fkey_style = 303451) -> Hash (cost=2.21..2.21 rows=121 width=18) (actual time=0.432..0.432 rows=121 loops=1) -> Seq Scan on opt_kind k (cost=0.00..2.21 rows=121 width=18) (actual time=0.042..0.196 rows=121 loops=1) -> Hash (cost=8.80..8.80 rows=480 width=31) (actual time=1.687..1.687 rows=480 loops=1) -> Seq Scan on opt_header h (cost=0.00..8.80 rows=480 width=31) (actual time=0.030..0.748 rows=480 loops=1) Total runtime: 20.893 ms (15 rows)
发生了什么,我该如何解决？我使用Postgresql 8.4.8.这是实际的观点：
SELECT o.fkey_style,h.name AS header,k.name AS kind,o.code,o.name AS option_name,o.description,count(*) OVER (PARTITION BY h.name) AS header_count,count(*) OVER (PARTITION BY h.name,k.name) AS header_kind_count FROM chrome_nvd.options o JOIN chrome_nvd.opt_header h ON h.id = o.fkey_opt_header JOIN chrome_nvd.opt_kind k ON k.id = o.fkey_opt_kind ORDER BY o.sequence;
< x> I think that’s just an implementation limitation
< EvanCarroll> x: I wonder what would have to be done to push the
WHERE clause down in this case.< EvanCarroll> the planner would have to know that the WindowAgg doesn’t itself add selectivity and therefore it is safe to push the WHERE down?
< x> EvanCarroll; a lot of very complicated work with the planner,I’d presume
和,
< a> EvanCarroll: nope. a filter condition on a view applies to the output of the view and only gets pushed down if the view does not involve aggregates
