The NOT NULL constraint is a type of constraint that is applied only to columns.
It checks whether a column contains any NULL values or not.
Here, a NULL value means a missing or unknown value.
If any attempt is made to insert a NULL value into that column, it will result in an error.
for example:
Suppose you define a column name as VARCHAR(100) NOT NULL.
This means every row must have a value in the name column — leaving it blank or inserting NULL will cause an error.
Syntax:
CREATE TABLE table_name (
column_name data_type NOT NULL
);
Example:
CREATE TABLE Employees (
employee_id INT PRIMARY KEY,
name VARCHAR(100) NOT NULL
);
Note: In this example, the name column cannot have NULL values.
Every record must have a value for the name field.