From: | Bruce Momjian <maillist(at)candle(dot)pha(dot)pa(dot)us> |
---|---|
To: | Leon <leon(at)udmnet(dot)ru> |
Cc: | "'pgsql-general(at)hub(dot)org'" <pgsql-general(at)hub(dot)org> |
Subject: | Re: [GENERAL] Fast join |
Date: | 1999-06-29 16:50:28 |
Message-ID: | 199906291650.MAA05952@candle.pha.pa.us |
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Lists: | pgsql-general |
> But look here:
> -------------
> adb=> EXPLAIN SELECT * FROM atable WHERE atable.cfield = btable.cfield AND
> atable.afield IN (SELECT btable.bfield WHERE btable.bfield=10);
> NOTICE: QUERY PLAN:
>
> Hash Join (cost=1483.00 rows=10000 width=24)
> -> Seq Scan on atable (cost=399.00 rows=10000 width=20)
> SubPlan
> -> Index Scan using gindex on btable (cost=2.05 rows=1 width=4)
> -> Hash (cost=399.00 rows=10000 width=4)
> -> Seq Scan on btable (cost=399.00 rows=10000 width=4)
> -------------
You can't use in index here because an IN is not selective, or if it is,
there is way for the optimizer to know this.
--
Bruce Momjian | http://www.op.net/~candle
maillist(at)candle(dot)pha(dot)pa(dot)us | (610) 853-3000
+ If your life is a hard drive, | 830 Blythe Avenue
+ Christ can be your backup. | Drexel Hill, Pennsylvania 19026
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