Null value

Null Value

A Null Value is a special marker used in Structured Query Language (SQL) to indicate that a data value does not exist in the database. Introduced by the creator of the relational database model, Edgar F. Codd, null value is a concept that addresses the absence of value or the presence of unknown value in the database.

Definition

In Database Management System (DBMS), null value is a condition that is used to represent the absence of any data value. It is important to note that a null value is different from a zero value or a field that contains spaces. A field with a null value is one that has been left blank during record creation.

Usage

Null values are used in SQL and other DBMS languages to handle situations where information is missing or not applicable. They can be the result of:

• Initial creation of a table where some columns are optional.
• Update of a table row that sets some columns to null.
• A join operation that does not find a matching row.

Handling Null Values

In SQL, null values are handled differently than other values. SQL provides two special functions, IS NULL and IS NOT NULL, to test whether a particular value is null or not. It also provides the COALESCE function to replace null values with a specified value.

Null Value in Programming Languages

In many Programming Languages, such as Java, C++, and Python, null value is used to represent the absence of a value or to mark uninitialized variables. It is often used to denote the end of a list in data structures.

See Also

• SQL
• Database Management System
• Edgar F. Codd
• Programming Languages