Beginner

81. NULL Value

Understand what NULL means in SQL and how missing or unknown values are represented.

📘 Lesson 81 of 728 ⏱ 7 min 🎯 Beginner

NULL represents a missing, unknown, or unavailable value in SQL. NULL is not the same as zero, an empty string, or a blank value. It indicates that a value is not currently available or is not known.

Real-world databases frequently contain missing information. Understanding NULL is essential for accurate filtering, calculations, reporting, and data-quality analysis.

An employee record may have a NULL value in the ManagerID column when the employee does not currently have a manager assigned.

SQL 
SELECT
    EmployeeName,
    ManagerID
FROM Employees;

NULL values commonly appear in customer data, employee records, financial systems, transaction data, and operational databases.

  • NULL represents missing or unknown information.
  • NULL is not the same as zero.
  • NULL is not the same as an empty string.
  • NULL requires special comparison rules.
  • SQL provides functions and operators for handling NULL.
What does NULL mean in SQL?

NULL represents a missing, unknown, or unavailable value.

Is NULL the same as zero?

No. NULL represents missing or unknown information, while zero is a valid numeric value.

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