Theoretical definition for the number of unique values?

[sqlservernewbie]

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!

[Larry Coon]

sq*************@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

[hpuxrac]

On Apr 12, 11:47 am, [e-mail] 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

[The Boss]

sq*************@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

[David Kerber]

In article <46*********************@news.xs4all.nl>,
us****@No.Spam.Please.invalid says...

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

[Gord]

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

In article <461e877b$0$328$[e-mail]>,
[e-mail] says...

[e-mail] 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).

[Martijn Tonies]

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.

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

[David Kerber]

In article <46***********************@dreader14.news.xs4all.n l>,
m.******@upscene.removethis.com says...

>

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.

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).

[DA Morgan]

David Kerber wrote:

>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??

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
da******@x.washington.edu
(replace x with u to respond)
Puget Sound Oracle Users Group
www.psoug.org