16.10 - Selectivity of Indexes - Teradata Database

Teradata Database SQL Fundamentals

Teradata Database
Release Number
Release Date
June 2017
Content Type
Programming Reference
Publication ID
English (United States)

An index that retrieves many rows is said to have weak selectivity.

An index that retrieves few rows is said to be strongly selective.

The more strongly selective an index is, the more useful it is. In some cases, it is possible to link together several weakly selective nonunique secondary indexes by bit mapping them. The result is effectively a strongly selective index and a dramatic reduction in the number of table rows that must be accessed.