This topic explains how to derive column demographics and how to add that information to the Table form.
Capture demographic data only for access and join column sets and primary key column sets.
By collecting this information, you are emulating some of the fundamental data collection activities performed by the COLLECT STATISTICS statement. The data is used for similar purposes as well: to help you to model your physical database in a way that its performance across all systems and applications is optimal.
Sources for the Required Information
The following table points to the sources for the data demographics requested by the Table form:
| Information | Source |
|---|---|
| Distinct values | Varies. This parameter determines how many unique values (including nulls) exist for the specified column.
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| Maximum rows/value | Varies. This parameter determines the maximum value for the specified column.
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| Rows/null | This parameter determines how many rows are null for the specified column.
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| Typical rows/value | This parameter determines a typical number of rows per value for the specified column. The typical number of rows per value for a column is not necessarily the average value, and the frequency can be so widely dispersed that a reasonably typical value cannot be determined. For information on examples of how to determine a value for this parameter, see Maximum and Typical Column Value Frequencies. |
| Change rating | Varied, depending on how your company operates. The following items are all likely sources for this information.
Note that the Teradata Index Wizard uses column change ratings as a parameter in determining the candidacy of columns for use as indexes. See the following topics for more information about how the Teradata Index Wizard uses this information:
The change rating codes are as follows.
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