I was surprised to hear that JOIN syntax constrained the planner. We
have a policy of using JOIN syntax to describe the table relationships
and where clauses to describe the selection process for our queries. It
was our understanding that the JOIN syntax was introduced to support
this approach, but not to contrain the planner.
Is there any way to sell the planner to consider JOIN syntax as
equivalent to WHERE clauses and to not use them to force the planner
down a specific path? Can we get that added as an option (and then made
available to use JDBC folks as a URL parameter). It would make my team
very happy :-).
I think that making this an option will help all those migrating to
Postgres who did not expect that JOINs forced the planner down specific
plans. Is it possible/reasonable to add?
Charlie
Tom Lane wrote:
>"Roman Fail" <rfail@posportal.com> writes:
>
>
>>Thanks to everyone for the quick replies! I'm sure that my lack of
>>skill with SQL queries is the main problem. What's strange to me is
>>how MSSQL takes my bad queries and makes them look good anyway. It
>>must have a real smart planner.
>>
>>
>
>I think more likely the issue is that your use of JOIN syntax is forcing
>Postgres into a bad plan. MSSQL probably doesn't assign any semantic
>significance to the use of "a JOIN b" syntax as opposed to "FROM a, b"
>syntax. Postgres does. Whether this is a bug or a feature depends on
>your point of view --- but there are folks out there who find it to be
>a life-saver. You can find some explanations at
>http://www.ca.postgresql.org/users-lounge/docs/7.3/postgres/explicit-joins.html
>
>
>
>>Is it pretty much universally accepted that I should drop all my
>>foreign keys?
>>
>>
>
>No. They don't have any effect on SELECT performance in Postgres.
>They will impact update speed, but that's not your complaint (at the
>moment). Don't throw away data integrity protection until you know
>you need to.
>
> regards, tom lane
>
>---------------------------(end of broadcast)---------------------------
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>
>
--
Charles H. Woloszynski
ClearMetrix, Inc.
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