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List:       postgresql-sql
Subject:    Re: [SQL] triple self-join crawling
From:       T E Schmitz <mailreg () numerixtechnology ! de>
Date:       2007-03-19 16:10:57
Message-ID: 45FEB611.8070606 () numerixtechnology ! de
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T E Schmitz wrote:
> T E Schmitz wrote:
> 
> Things improved hugely when I changed the JOIN clauses:

see explain analyze below - can this be improved further?

> 
> LEFT OUTER JOIN history AS past_month ON (past_month.stock = 
> history.stock        AND past_month.day >= (history.day - 30) AND 
> past_month.day < history.day)
> LEFT OUTER JOIN history AS past_week  ON (past_week.stock   = 
> past_month.stock AND past_week.day  =past_month.day AND past_week.day >= 
> (history.day - 7))

QUERY PLAN
GroupAggregate  (cost=1370368.19..1435888.88 rows=5801 width=56) (actual 
time=11945.030..13163.156 rows=5801 loops=1)
   ->  Sort  (cost=1370368.19..1379715.86 rows=3739067 width=56) (actual 
time=11944.753..12462.623 rows=120117 loops=1)
         Sort Key: history.stock, history."day", history.high, history.low
         ->  Hash Left Join  (cost=160.02..391554.63 rows=3739067 
width=56) (actual time=52.746..3778.409 rows=120117 loops=1)
               Hash Cond: ((("outer".stock)::text = 
("inner".stock)::text) AND ("outer"."day" = "inner"."day"))
               Join Filter: ("inner"."day" >= ("outer"."day" - 7))
               ->  Nested Loop Left Join  (cost=0.00..204441.26 
rows=3739067 width=57) (actual time=0.077..2313.375 rows=120117 loops=1)
                     Join Filter: (("inner".stock)::text = 
("outer".stock)::text)
                     ->  Seq Scan on history  (cost=0.00..131.01 
rows=5801 width=34) (actual time=0.016..34.845 rows=5801 loops=1)
                     ->  Index Scan using idx_history_day on history 
past_month  (cost=0.00..22.32 rows=645 width=23) (actual 
time=0.020..0.185 rows=21 loops=5801)
                           Index Cond: ((past_month."day" >= 
("outer"."day" - 30)) AND (past_month."day" < "outer"."day"))
               ->  Hash  (cost=131.01..131.01 rows=5801 width=23) 
(actual time=52.608..52.608 rows=5801 loops=1)
                     ->  Seq Scan on history past_week 
(cost=0.00..131.01 rows=5801 width=23) (actual time=0.010..25.110 
rows=5801 loops=1)

Total runtime: 13187.729 ms
-- 


Regards,

Tarlika Elisabeth Schmitz

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