Beginner

337. NULL Handling

Understand how SQL represents missing or unknown values and how to work with them safely.

📘 Lesson 337 of 728 ⏱ 10 min 🎯 Beginner

NULL represents a missing, unknown, or unavailable value. NULL is not the same as zero, an empty string, or a normal value.

Incorrect NULL handling can produce unexpected query results, inaccurate calculations, and misleading reports.

Find employees whose manager information is missing.

SQL 
SELECT
    EmployeeName,
    ManagerID
FROM Employees
WHERE ManagerID IS NULL;

NULL handling is essential in customer data, financial reporting, employee records, transactions, and data-quality analysis.

  • NULL represents missing or unknown information.
  • NULL is not equal to zero.
  • NULL is not normally compared using =.
  • Use IS NULL to test for NULL.
  • Use COALESCE or similar functions for fallback values.
What is NULL in SQL?

NULL represents a missing, unknown, or unavailable value.

Can you use ManagerID = NULL?

No. SQL uses IS NULL or IS NOT NULL to test for NULL values.

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