16.10 - Duplicate Rows in Tables - Teradata Database

Teradata Database SQL Fundamentals

Product
Teradata Database
Release Number
16.10
Release Date
June 2017
Content Type
Programming Reference
Publication ID
B035-1141-161K
Language
English (United States)

Though both set theory and common sense prohibit duplicate rows in relational tables, the ANSI standard defines SQL based not on sets, but on bags, or multisets.

A table defined not to permit duplicate rows is called a SET table because its properties are based on set theory, where set is defined as an unordered group of unique elements with no duplicates.

A table defined to permit duplicate rows is called a MULTISET table because its properties are based on a multiset, or bag, model, where bag and multiset are defined as an unordered group of elements that may be duplicates.