Semantics of SQL Nulls | Database Design | Teradata Vantage - 17.10 - Semantics of SQL Nulls - Advanced SQL Engine - Teradata Database

Teradata Vantage™ - Database Design

Product
Advanced SQL Engine
Teradata Database
Release Number
17.10
Release Date
July 2021
Content Type
User Guide
Publication ID
B035-1094-171K
Language
English (United States)

For most applications, an SQL null means that the value of interest is not known. The only exceptions to this occur when nulls are used to represent the empty set. SQL does not support the empty set.

Types of Missing Values

The following list touches on most of the common uses of SQL nulls:

  • Value is unknown
  • Value is not applicable
  • Value does not exist
  • Value is not defined
  • Value is not valid
  • Value is not supplied
  • Value is the empty set

The semantics, properties, and behavior of each of these null types are different, but SQL treats them identically, including all 14 of the ANSI/X3/SPARC “null manifestations” and their 8 submanifestations.