Hi Mohamed,
in addition to Martin's reply.
Please also consider daft data types - especially in case of VARCHAR2, which
maybe used wrongly for date values for example. The CBO calculations can
be wrong very easily in combination with range based predicates.
Jonathan Lewis described this in his book "Cost-Based Oracle Fundamentals" very
carefully on page 175 ("Data Problems Revisited").
Best Regards
Stefan Koehler
Oracle performance consultant and researcher
Homepage: http://www.soocs.de
Twitter: @OracleSK
> Mohamed Houri <mohamed.houri@xxxxxxxxx> hat am 31. Oktober 2014 um 12:06
> geschrieben:
>
> Dears,
> What benefit the CBO can gain from a unique varchar2 column having height
> balanced histogram (11.2.0.3.0) ?
> Thanks
> --
> Houri Mohamed
> Oracle DBA-Developer-Performance & Tuning
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