Re: Joining 16 tables seems slow

On 09/12/2017 01:45 AM, Frank Millman wrote:
> Hi all
> I am using 9.4.4 on Fedora 22.
> 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.
> My test involves selecting a single row. Both versions work. The first
> version takes 0.06 seconds. The second takes 0.23 seconds. On further
> experimentation, the time for the second one seems to taken in setting up
> the joins, because if I omit selecting anything from the joined tables, it
> still takes 0.23 seconds.
> Exactly the same exercise on Sql Server results in 0.06 seconds for both
> versions.
> I realise that, if I was selecting a large number of rows, 0.23 seconds is
> trivial and the overall result could be different. But still, it seems odd.

Just out of curiosity, what if you PREPARE the statement, and take multiple
timings?

--
World Peace Through Nuclear Pacification