Re: Unions and Grouping
От | Ragnar |
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Тема | Re: Unions and Grouping |
Дата | |
Msg-id | 1166221809.6369.202.camel@localhost.localdomain обсуждение исходный текст |
Ответ на | Re: Unions and Grouping ("Aaron Bono" <postgresql@aranya.com>) |
Ответы |
Re: Unions and Grouping
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Список | pgsql-sql |
On fös, 2006-12-15 at 16:17 -0600, Aaron Bono wrote: > On 12/15/06, Tom Lane <tgl@sss.pgh.pa.us> wrote: > "Aaron Bono" <postgresql@aranya.com> writes: > > My question, what do the SQL Specifications say should > happen on a Union? > > Is it supposed to eliminate duplicates even WITHIN the > individual queries > > that are being unioned? > > Yes. SQL92 7.10 saith: > [snip SQL92 standardese] > > So if I don't want the duplicated WITHIN the two queries to be > eliminated, I use UNION ALL? with UNION ALL, no duplicates will be discarded, either "within" or "between" the queries. if I understand you, you are looking for having only queries that are both in Q1 and Q2 removed, but not for example, any duplicates in Q1 that are not in Q2. if this is what you want, then I think you may not have thought it through. what about a row that is twice in Q1 and three times in Q2? how many copies of this row should be in the result? gnari
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