From: | Thomas Lockhart <lockhart(at)alumni(dot)caltech(dot)edu> |
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To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | pgsql-hackers(at)postgreSQL(dot)org |
Subject: | Re: A fine point about OUTER JOIN semantics |
Date: | 2000-09-04 18:25:28 |
Message-ID: | 39B3E918.2D869F2B@alumni.caltech.edu |
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Thread: | |
Lists: | pgsql-hackers |
> > In some cases, an outer join with WHERE restrictions reduces to
> > an inner join (so the qualification clauses can be consolidated).
> I recall you having muttered something about that before, but I don't
> see how it works. Can you give an example of an outer join that
> reduces to an inner join?
Hmm. This example is pretty silly, but afaik it reduces to an inner
join:
select i, j from t1 left join t2 using (i) where j is not null;
(where t1 has column "i" and t2 has columns "i" and "j").
- Thomas
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