Re: cross column correlation revisted

2010/7/14 Tom Lane <tgl@sss.pgh.pa.us>:
> If the combination of columns is actually interesting, there might well
> be an index in place, or the DBA might be willing to create it.

Indexes aren't free, though, nor even close to it.

Still, I think we should figure out the underlying mechanism first and
then design the interface afterwards.  One idea I had was a way to say
"compute the MCVs and histogram buckets for this table WHERE
<predicate>".  If you can prove predicate for a particular query, you
can use the more refined statistics in place of the full-table
statistics.  This is fine for the breast cancer case, but not so
useful for the zip code/street name case (which seems to be the really
tough one).

-- 
Robert Haas
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