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!

sqlservernewbie@yahoo.com wrote:

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?

Using your definitions, it'd probably be "the cardinality of the
domain."


Larry Coon
University of California

On Apr 12, 11:47 am, 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!

distinct values

For a column or set of columns which together an index is created from
you can think of it as distinct keys

sqlservernewbie@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.

--
Jeroen

In article <461e877b$0$328$e4fe514c@news.xs4all.nl>,
usenet@No.Spam.Please.invalid says...

sqlservernewbie@yahoo.com wrote:

>
(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?


--
Remove the ns_ from if replying by e-mail (but keep posts in the
newsgroups if possible).

On Apr 12, 4:14 pm, David Kerber
<ns_dkerber@ns_WarrenRogersAssociates.comwrote:

In article <461e877b$0$328$e4fe5...@news.xs4all.nl>,
use...@No.Spam.Please.invalid says...
>
>
>

>

>

>

>

>

>

>

>

>

>

>

>

>

>

>

>
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).

>
I believe that one of the cardinal rules (pun intended) of RDBMS
theory is that a table can never have duplicate rows.

True. There's no point in having duplicate rows, cause you can't tell
which one you're handling :-)



--
Martijn Tonies
Database Workbench - development tool for MySQL, and more!
Upscene Productions
http://www.upscene.com
My thoughts:
http://blog.upscene.com/martijn/
Database development questions? Check the forum!
http://www.databasedevelopmentforum.com

In article <461f2fcd$0$11982$e4fe514c@dreader14.news.xs4all.n l>,
m.tonies@upscene.removethis.com says...

>

>
True. There's no point in having duplicate rows, cause you can't tell
which one you're handling :-)

True, but are you telling me you've never had it happen accidentally??


--
Remove the ns_ from if replying by e-mail (but keep posts in the
newsgroups if possible).

David Kerber wrote:

>
True, but are you telling me you've never had it happen accidentally??

Assuming the database is being used as more than an electronic form
of Excel or 3x5 cards ... no. Primary key constraints were invented
for a reason. Like seat belts they are most useful when used.
--
Daniel A. Morgan
University of Washington
damorgan@x.washington.edu
(replace x with u to respond)
Puget Sound Oracle Users Group
www.psoug.org