| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | "Tambet Matiisen" <t(dot)matiisen(at)aprote(dot)ee> |
| Cc: | ch(at)rodos(dot)fzk(dot)de, pgsql-sql(at)postgresql(dot)org |
| Subject: | Re: How to force subquery scan? |
| Date: | 2005-03-16 15:41:52 |
| Message-ID: | 6303.1110987712@sss.pgh.pa.us |
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| Lists: | pgsql-sql |
"Tambet Matiisen" <t(dot)matiisen(at)aprote(dot)ee> writes:
> It seems that subquery scan is only used, when the query can not be
> translated into single flat query. Which is mostly good, I assume.
The planner thinks so anyway ;-)
If you're desperate you can put in an optimization fence, for instance
LIMIT or OFFSET.
SELECT * FROM (SELECT ... OFFSET 0) ss;
In principle the planner could figure out that this offset is a no-op,
throw it away, and then flatten the query. But it doesn't at the
moment, and I doubt we'll teach it to do so in the future.
regards, tom lane
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