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RE: Density calculation. Was: Incorrect cardinality estimate

From: Laimutis Nedzinskas <Laimutis.Nedzinskas_at_landsbanki.is>
Date: Thu, 25 Jan 2007 14:43:29 -0000
Message-ID: <5A8896FB2AFC5445A7DCFC5903CCA6B06FEC79@W03856.li01r1d.lais.net>


In the other words Oracle is using histogram in the best way it can:

-----Original Message-----
From: oracle-l-bounce_at_freelists.org
[mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Wolfgang Breitling

For a height-balanced histogram the (non-null) column values are sorted and then "filled" into buckets of num_non_null_rows/buckets rounded
(most likely up) to an integer. Then the first value, the highest value
in each bucket, and the last value are recorded. Popular values are those that occur as the highest value in more than one (consecutive) bucket.
Fyrirvari/Disclaimer
http://www.landsbanki.is/disclaimer

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Received on Thu Jan 25 2007 - 08:43:29 CST

Original text of this message

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