Re: SQL compatibility reminder: MySQL vs PostgreSQL
От | Pierre C |
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Тема | Re: SQL compatibility reminder: MySQL vs PostgreSQL |
Дата | |
Msg-id | op.u88thxfieorkce@localhost обсуждение исходный текст |
Ответ на | Re: SQL compatibility reminder: MySQL vs PostgreSQL (Marko Tiikkaja <marko.tiikkaja@cs.helsinki.fi>) |
Ответы |
Re: SQL compatibility reminder: MySQL vs PostgreSQL
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Список | pgsql-hackers |
> As far as I can tell, we already do index skip scans: This feature is great but I was thinking about something else, like SELECT DISTINCT, which currently does a seq scan, even if x is indexed. Here is an example. In both cases it could use the index to skip all non-interesting rows, pulling only 69 rows from the heap instead of 120K. EXPLAIN ANALYZE SELECT DISTINCT vente, type_id FROM annonces; QUERYPLAN ----------------------------------------------------------------------------------------------------------------------- HashAggregate (cost=15270.98..15271.82 rows=84 width=3) (actual time=113.277..113.288 rows=69 loops=1) -> Seq Scan on annonces (cost=0.00..14682.32 rows=117732 width=3) (actual time=0.005..76.069 rows=119655 loops=1) EXPLAIN ANALYZE SELECT DISTINCT ON( vente, type_id ) * FROM annonces; QUERY PLAN ------------------------------------------------------------------------------------------------------------------------------------------------ Unique (cost=0.00..34926.90 rows=84 width=1076) (actual time=0.019..107.318 rows=69 loops=1) -> Index Scan using annonces_type on annonces (cost=0.00..34338.24 rows=117732 width=1076) (actual time=0.017..52.982 rows=119655 loops=1)
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