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?
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World Peace Through Nuclear Pacification
