| From: | Taral <taral(at)taral(dot)net> |
|---|---|
| To: | Thomas Lockhart <lockhart(at)alumni(dot)caltech(dot)edu> |
| Cc: | Bruce Momjian <maillist(at)candle(dot)pha(dot)pa(dot)us>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: [HACKERS] Oops, I seem to have changed UNION's behavior |
| Date: | 1999-05-09 20:52:17 |
| Message-ID: | Pine.LNX.4.10.9905091551330.8677-100000@dragon.taral.net |
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| Lists: | pgsql-hackers |
On Sun, 9 May 1999, Thomas Lockhart wrote:
> > > Am I right in thinking that UNION (without ALL) is defined to do a
> > > DISTINCT on its result, so that duplicates are removed even if the
> > > duplicates both came from the same source table? That's what 6.4.2
> > > does, but I do not know if it's strictly kosher according to the SQL
> > > spec.
>
> Yes, this is the right behavior according to SQL92...
In which case something should put a DISTINCT on queries using UNION...
since making T_Query nodes never equal is a deoptimization.
Taral
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