17.05 - Unconstrained Joins - Advanced SQL Engine - Teradata Database

Teradata Vantage™ - SQL Data Manipulation Language

Advanced SQL Engine
Teradata Database
Release Number
Release Date
January 2021
Content Type
Programming Reference
Publication ID
English (United States)

An unconstrained join is one for which a WHERE clause is not specified for the tables that are joined. See Cross Join.

The result of an unconstrained join is a Cartesian product, which is rarely the desired result. A Cartesian product is the product of the number of rows in each table that is joined. An unconstrained join can produce a great many rows, returning a result that not only is not desired, but one that places a large performance burden on the system.

If a SELECT statement specifies correlation and real names (for example, correlation names in a WHERE clause and real names in the select list), the Optimizer may specify an unconstrained join, depending on what the conditions of the query are and how they are specified.