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Posted by Gord on 04/12/07 22:12
On Apr 12, 4:14 pm, David Kerber
<ns_dkerber@ns_WarrenRogersAssociates.com> wrote:
> In article <461e877b$0$328$e4fe5...@news.xs4all.nl>,
> use...@No.Spam.Please.invalid says...
>
>
>
> > sqlservernew...@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: M, F.
> > > The result is 2 unique values.
>
> > > What do we call this concept?
> > > "the number of unique values in a column?"
>
> > > Is there one?
>
> > > Thanks a lot!
>
> > (Column) Cardinality = number of distinct column/attribute values.
> > Table Cardinality = number of rows in a table.
>
> Shouldn't that be *distinct* (non-duplicate) rows in the table?
I believe that one of the cardinal rules (pun intended) of RDBMS
theory is that a table can never have duplicate rows.
> --
> Remove the ns_ from if replying by e-mail (but keep posts in the
> newsgroups if possible).
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