Re: Wrong estimate in query plan

Eelke Klein wrote
> What I noticed is that are no most common values mentioned ofcourse the
> value 1 only occurs once in the column but as all other values are NULL
> you
> could argue it is a common value.

A random sampling is unlikely to choose a record that only appears in 0.1
percent of the table.

Two sequential scans plus a hash seems like a good plan.

The smaller table is so small a sequential scan is fast. The larger table
experts to have all records read so it to should be scanned.  Combining with
a hash seems sound.  The fact the cross-column estimate is way off isn't
that big a deal though I'd be curious to hear Tom's opinion on why this is
so for educational purposes.

David J.




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