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126. NULL Handling

Understand common techniques for identifying, replacing, and working with NULL values.

📘 Lesson 126 of 728 ⏱ 9 min 🎯 Intermediate

NULL handling refers to the techniques used to identify, replace, compare, exclude, or otherwise manage missing or unknown values in SQL queries.

Real-world datasets frequently contain missing information. Poor NULL handling can produce incorrect calculations, incomplete reports, and misleading business conclusions.

An analyst calculating average salary must understand how NULL salary values are treated by the database.

SQL 
SELECT
    AVG(COALESCE(Salary, 0)) AS AverageSalary
FROM Employees;

NULL handling is important in financial analysis, customer reporting, employee analytics, data cleaning, and dashboard preparation.

  • NULL represents missing or unknown information.
  • Use IS NULL to find NULL values.
  • Use IS NOT NULL to exclude NULL values.
  • COALESCE can provide fallback values.
  • NULLIF can convert matching values to NULL.
  • NULL behavior matters in calculations.
Why is NULL handling important?

It prevents missing values from producing unexpected filtering, calculation, and reporting results.

Name two SQL techniques for handling NULL.

IS NULL can identify NULL values, while COALESCE can replace NULL with a fallback value.

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