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Re: Theoretical definition for the number of unique values?

From: Cimode <cimode_at_hotmail.com>
Date: 13 Apr 2007 07:26:42 -0700
Message-ID: <1176474402.335403.8500@y5g2000hsa.googlegroups.com>


On Apr 12, 4:19 pm, sqlservernew..._at_yahoo.com wrote:
> Hi Everyone,
>
> Here is a theoretical, and definition question for you.
>
> In databases, we have:
>
> Relation
> a table with columns and rows
>
> Attribute
> a named column/field of a relation
>
> Domain
> a set of allowable values for one or more attributes
>
> Tuple
> a row of a relation
>
> Degree
> the number of attributes a relation contains
> Number of fields in a table
>
> Cardinality
> the number of tuples/rows a relation contains
>
> But!
>
> What is the definition for the number of unique values in a field?
>
> So, if you have 100 rows in a table, and the field is
> the gender field, with only values of: Y, N.
> You have 2 unique values.
>
> What do we call this concept?
> "the number of unique values in a column?"
>
> Is there one?
>
> Thanks a lot!

I do not believe there is a specific terminology or usefulness for such concept. You may call it *domain attribute projection cardinality* (I just made it up but it could be a description of underlying concepts). Received on Fri Apr 13 2007 - 09:26:42 CDT

Original text of this message

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