Re: [GENERAL] Joining 16 tables seems slow

"Frank Millman" <frank@chagford.com> writes:
> Pavel Stehule wrote:
>> 2017-09-12 8:45 GMT+02:00 Frank Millman <frank@chagford.com>:
>>>   I am experimenting with optimising a SQL statement. One version uses 4 LEFT JOIN’s and a 5-way CASE statement in
thebody. 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.)
        regards, tom lane


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