Gregory Stark wrote:
I wonder if it would be more worthwhile to remove them and have a subsequent
phase where we look for possible joins to *add*. So even if the user writes
"select * from invoices where customer_id=?" the planner might be able to
discover that it can find those records quicker by scanning customer, finding
the matching <company_id,customer_id> and then using an index to look them up
in invoices.


Yeah, that would be cool. The question is whether it's worth the additional overhead in planner, compared to the gain in the rare case that it's applicable. That's always the thing with planner tricks like this. I think we'll eventually need some sort of tuning knob to control how hard the planner tries to apply different optimizations like that.

--
  Heikki Linnakangas
  EnterpriseDB   http://www.enterprisedb.com

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