16.10 - Duplicate Rows in Tables - Teradata Database

Teradata Database SQL Fundamentals

Product
Teradata Database
Release Number
16.10
Published
June 2017
Content Type
Programming Reference
Publication ID
B035-1141-161K
Language
English (United States)
Last Update
2018-04-25

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.