15.00 - Sources for the Required Information - Teradata Database

Teradata Database Design

prodname
Teradata Database
vrm_release
15.00
category
User Guide
featnum
B035-1094-015K

Sources for the Required Information

The following table points to the sources for the multicolumn data demographics requested by the Table form. With the exception of the information documented here, sources are identical to those documented by “Sources for the Required Information” on page 158.

 

Information

Source

Distinct values

See the following topics.

  • “Calculating Multicolumn Demographics” on page 168
  • “Example Cases for These Guidelines” on page 168
  • Maximum rows/value

    Rows/null

    Typical rows/value

    Example  

    This example form, which continues the form illustrated in “Table Form Example” on page 154 indicates two multicolumn index candidates.

    Information acquisition for the second of the two multicolumn specifications is made more simple because the specified columns constitute the primary key for the table.

    Because the index candidates are both composite, you cannot use an identity column to define them.

    This implies certain demographics by default, as described by the following list. The listed implications hold true irrespective of whether the primary key is uni- or multicolumnar.

  • All demographics must be unique.
  • No demographics can be null.
  • Therefore, the value for Rows Null is always 0.

  • The value for Distinct Values always matches the Cardinality for the table and the value for Maximum Rows/Value is always 1.
  • Note that the value for Change Rating is also 0 by default because primary key values should never be changed.

     

    Table, continued

    (Multicolumn index considerations)

    Page:   of

            ELDM Page: 

            System: Patient Tracking

    Table Name:

    Patient_Service_History

    Table Type: History

    Cardinality: 730,000

    Data Protection: RAID 5

    Column Name

    Patient_ID

    Service_ID

    Patient_ID

    Service_ID

    Timestamp

     

    PK/FK/ID

    FK

    PK

     

     

     

     

     

    Constraint Number

     

     

     

    Value Access Frequency

     

                120,000

     

    Join Access Frequency

                     2,200

                300,000

     

    Join Access

    Rows

                 200,000

                300,000

     

    Distinct Values

                     8,000

                730,000

     

    Maximum Rows/Value

                        365

                            1

     

    Maximum Rows Null

                            0

                            0

     

    Typical Rows/Value

                          90

                            1

     

    Change Rating

                            0

                            0

     

    PI/SI