Re: Height Balanced Histogram on a unique varchar2 column
- From: Sayan Sergeevich Malakshinov <malakshinovss@xxxxxxxxx>
- To: mohamed.houri@xxxxxxxxx
- Date: Fri, 31 Oct 2014 14:26:57 +0300
> Mohamed Houri <mohamed.houri@xxxxxxxxx>
>
> What benefit the CBO can gain from a unique varchar2 column having
> height balanced histogram (11.2.0.3.0) ?
CBO doesn't know real logic, so it can assume that you have queries with
"like", "substr", "<=", "between".
> create table t1
> (col1 number
> ,col2 varchar2(50)
> ,flag varchar2(2));
Also, as i remember, CBO stores only first 30 chars for varchar2 columns
in the histograms and high/low values.
--
Best regards,
Sayan Malakshinov
http://orasql.org
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