Selectivity of Indexes - Advanced SQL Engine - Teradata Database

SQL Fundamentals

Product
Advanced SQL Engine
Teradata Database
Release Number
17.05
17.00
Published
June 2020
Language
English (United States)
Last Update
2021-01-24
dita:mapPath
zwv1557098532464.ditamap
dita:ditavalPath
lze1555437562152.ditaval
dita:id
B035-1141
lifecycle
previous
Product Category
Teradata Vantageâ„¢

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.