From: Steve Edberg
Date: April 14 1999 11:33pm
Subject: Re: How to get index/key information via C interface.
List-Archive: http://lists.mysql.com/mysql/1870
Message-Id: <199904142334.QAA18533@franc.ucdavis.edu>
MIME-Version: 1.0
Content-Type: text/plain; charset="us-ascii"

>On Wed, Apr 14, 1999 at 06:50:12PM -0500, Benjamin Scherrey wrote:
>> So I have to parse the results table? OK I guess.
>
<SNIP>
>
>> Btw... what do the results named Collation, Cardinality, and
>> Sub_Part mean?
>
>I'm not really sure about this.  Looks like Collation is either
>"Ascending" or "Descending", but I don't know what that means.
>And Cardinality has to do with how MySQL optimizes queries - it
>has an idea of how the key values are distributed.  And Sub_Part
>has to do, I think, with only indexing the first part of a field
>(e.g., the first 20 characters of a VARCHAR field).


Cardinality is the number of unique values in the field; for instance, if
you had a 'sex' field, with only 'M' or 'F' values, that would have a
cardinality of 2.


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| Steve Edberg                           University of California, Davis |
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| (530) 753-7605                                           (530)754-9127 |
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