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130. NOT NULL Constraint

Learn how NOT NULL ensures that a column must contain a value.

📘 Lesson 130 of 728 ⏱ 8 min 🎯 Beginner

A NOT NULL constraint prevents a column from storing NULL values. It is used when a value is required for every row.

Required business information should not be missing. NOT NULL helps enforce this requirement at the database level.

An EmployeeName column should normally contain a value for every employee, so it can be defined as NOT NULL.

SQL 
CREATE TABLE Employees (
    EmployeeID INT NOT NULL,
    EmployeeName VARCHAR(100) NOT NULL,
    Salary DECIMAL(12,2)
);

NOT NULL is commonly used for names, identifiers, transaction dates, amounts, statuses, and other mandatory fields.

  • NOT NULL prevents NULL values.
  • It is used for required fields.
  • It helps maintain data quality.
  • It is defined at the column level.
  • It is commonly used with other constraints.
What does NOT NULL do?

NOT NULL prevents a column from containing NULL values.

Why use NOT NULL?

It ensures that required information is provided for every applicable record.

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