Perez wrote:
> I thought, from watching the list for a while, that the planner
> statistics needed were known but that how to gather the statistics
> was not?

I think over the course of the discussion we have figured out that we 
would like to have cross-column correlation statistics.  The precise 
mathematical incarnation hasn't been determined yet, as far as I can 
see.  Collecting the statistics thereafter isn't that hard, but there 
needs to be a way to not collect an exponential volume of statistics on 
all column combinations.

Peter Eisentraut

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TIP 9: In versions below 8.0, the planner will ignore your desire to
       choose an index scan if your joining column's datatypes do not

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