| From: | Thomas Lockhart <lockhart(at)alumni(dot)caltech(dot)edu> |
|---|---|
| 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: | 2000-09-02 06:20:26 |
| Message-ID: | 39B09C2A.FEBC6B85@alumni.caltech.edu |
| Views: | Raw Message | Whole Thread | Download mbox | Resend email |
| Thread: | |
| Lists: | pgsql-hackers |
> Am I right in thinking that the WHERE clause of a query must logically
> be applied *after* any joins specified in the FROM clause?
...
> This shows that JOIN/ON conditions for outer joins are not semantically
> interchangeable with WHERE conditions.
Right. In some cases, an outer join with WHERE restrictions reduces to
an inner join (so the qualification clauses can be consolidated). Our
optimizer should be on the lookout for that, at least eventually.
- Thomas
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