Re: Question About UNION
От | Bill Thoen |
---|---|
Тема | Re: Question About UNION |
Дата | |
Msg-id | 48EE387B.4030102@gisnet.com обсуждение исходный текст |
Ответ на | Re: Question About UNION (Raymond O'Donnell <rod@iol.ie>) |
Ответы |
Re: Question About UNION
Re: Question About UNION |
Список | pgsql-general |
Raymond O'Donnell wrote: > On 09/10/2008 17:36, Bill Thoen wrote: > >> I'm trying to combine two tables, but I only want unique records based >> on the first two columns. Can UNION be used to join three-column tables >> but only include records based on the uniqueness of the first two >> columns? If not, how would I do this with PostgreSQL 8.1? >> > > How do you decide which records you want? - e.g. given the following rows... > > (a, b, c) > (a, b, d) > > ...how do you decide whether you the one with c or the one with d? > > The physical order that they appear will take care of that.
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