Re: Joining 16 tables seems slow

2017-09-12 14:01 GMT+02:00 Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>:

> "Frank Millman" <frank(at)chagford(dot)com> writes:
> > Pavel Stehule wrote:
> >> 2017-09-12 8:45 GMT+02:00 Frank Millman <frank(at)chagford(dot)com>:
> >>> I am experimenting with optimising a SQL statement. One version uses
> 4 LEFT JOIN’s and a 5-way CASE statement in the body. The second moves the
> filtering into the JOIN section, and I end up with 16 LEFT JOIN’s and no
> CASE statements.
>
> >> you can experimentally try increase FROM_COLLAPSE_LIMIT to some higher
> number 14 maybe 16
>
> > I tried increasing FROM_COLLAPSE_LIMIT, but it made no difference.
>
> For this you need to increase join_collapse_limit, not
> from_collapse_limit. (Usually, though, there's little reason not to keep
> them the same.)
>

sure - my mistake - I though it.

Thank you

Pavel

>
> regards, tom lane
>
>
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