1.1 - 8.10 - Approximate Cardinality (ML Engine) - Teradata Vantage

Teradata Vantage™ - Machine Learning Engine Analytic Function Reference

Product
Teradata Vantage
Release Number
1.1
8.10
Published
October 2019
Content Type
Programming Reference
Publication ID
B700-4003-079K
Language
English (United States)
Last Update
2019-12-31

The Approximate Cardinality function, which is composed of the ApproxCardinalityReduce and ApproxCardinalityMap functions, can estimate the cardinality (number of distinct values) in a column or combination of columns, scanning the table only once.

Teradata recommends this function when the column or combination of columns has a large cardinality. When the cardinality is small, Teradata recommends the SQL SELECT DISTINCT command.

The function uses the Flajolet-Martin algorithm. For more information, see Probabilistic Counting Algorithms for Data Base Applications, by Philippe Flajolet and G. Nigel Martin (http://portal.acm.org/citation.cfm?id=5215).