| From: | Joachim Wieland <joe(at)mcknight(dot)de> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | David Wheeler <david(at)kineticode(dot)com>, pgsql-performance <pgsql-performance(at)postgresql(dot)org> |
| Subject: | Re: IMMUTABLE? |
| Date: | 2006-05-16 16:55:14 |
| Message-ID: | 20060516165514.GA4424@mcknight.de |
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| Lists: | pgsql-performance |
On Tue, May 16, 2006 at 09:33:14AM -0400, Tom Lane wrote:
> Joachim Wieland <joe(at)mcknight(dot)de> writes:
> > So irrespective of caching to prevent evaluation across statements, within a
> > single statement, is there a strong reason why for example in
> > WHERE col = f(const) with f() declared as immutable or stable and without an
> > index on col, f() still gets called for every row? Or is this optimization
> > just not done yet?
> The above statement is not correct, at least not for immutable functions.
So an immutable function gets evaluated once but a stable function still gets
called for every row? Wouldn't it make sense to call a stable function only
once as well?
Joachim
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