Details
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Improvement
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Status: Open
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Major
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Resolution: Unresolved
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None
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None
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Description
For Joins involving compound predicates, multi column stats can be used to accurately compute the NDV.
Objective is to compute NDV of more than one columns.
Compute NDV of (x,y,z).
R1 IJ R2 on R1.x=R2.x and R1.y=R2.y and R1.z=R2.z can use max(NDV(R1.x, R1.y, R1.z), NDV(R2.x, R2.y, R2.z)) for Join NDV (& hence selectivity).
http://www.oracle-base.com/articles/11g/statistics-collection-enhancements-11gr1.php#multi_column_statistics
http://blogs.msdn.com/b/ianjo/archive/2005/11/10/491548.aspx
http://developer.teradata.com/database/articles/removing-multi-column-statistics-a-process-for-identification-of-redundant-statist