NOT NULL constraint

A constraint is a restriction or business rule which can be imposed on the data for managing data integrity. When a business rule is imposed on the data, the data cannot violate the rule.

When NOT NULL constraint is imposed on a column the column will not allow NULL values into it.

Syntax:

Create Table <table_name> <column 1><data type> [width][NOT NULL],…. <column N>< data type>[width][NOT NULL]

Example:

Create Table BANK (Customerid Int NOT NULL, Cname varchar (50), Balance Decimal (7, 2) NOT NULL)

Note: When a NOT NULL constraint is imposed on a column the column will not allow NULL values but allows duplicate values.