17.05 - Unconstrained Joins - Advanced SQL Engine - Teradata Database

Teradata Vantage™ - SQL Data Manipulation Language

Product
Advanced SQL Engine
Teradata Database
Release Number
17.05
Release Date
January 2021
Content Type
Programming Reference
Publication ID
B035-1146-175K
Language
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.