Re: SQL challenge--top 10 for each key value?
От | Troels Arvin |
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Тема | Re: SQL challenge--top 10 for each key value? |
Дата | |
Msg-id | pan.2004.04.10.22.13.16.594061@arvin.dk обсуждение исходный текст |
Ответ на | SQL challenge--top 10 for each key value? (Jeff Boes <jboes@nexcerpt.com>) |
Ответы |
Re: SQL challenge--top 10 for each key value?
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Список | pgsql-sql |
On Fri, 09 Apr 2004 02:11:44 -0400, Tom Lane wrote: >> ROW_NUMBER() is a spec defined function. (6.10 of SQL200N) > > If the spec doesn't even have a year number yet, you can hardly expect > real implementations to support it ;-) SQL:2003 is finished. Among its new (non-core) OLAP features are a set of "windows functions" (spec section 6.10), which include feature ID T611 (elementary OLAP):- ROW_NUMBER() OVER (...)- RANK() OVER (...)- DENSE_RANK() OVER (...) feature ID T612 (extended OLAP):- PERCENT_RANK() OVER (...)- CUME_DIST() OVER (...) See http://www.acm.org/sigmod/record/issues/0403/index.html#standards for an article which summarizes the news in SQL:2003. ROW_NUMBER() OVER may be used in queries where a PostgreSQL user which use LIMIT. RANK() OVER may be used in queries where a PostgreSQL user would have to come up with a somewhat strange query in order to get acceptable performance, see http://troels.arvin.dk/db/rdbms/#select-top-n-postgresql -- Greetings from Troels Arvin, Copenhagen, Denmark
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