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89. NULL in GROUP BY

Understand how NULL values are handled when data is grouped using GROUP BY.

📘 Lesson 89 of 728 ⏱ 8 min 🎯 Beginner

When a column containing NULL values is used in GROUP BY, rows with NULL in that column are generally placed into one group representing the NULL value.

Grouped reports can contain missing categories. Understanding the NULL group helps analysts identify incomplete data and interpret summary reports correctly.

If some employees have no department assigned, GROUP BY Department can produce a group representing NULL department values.

SQL 
SELECT
    Department,
    COUNT(*) AS EmployeeCount
FROM Employees
GROUP BY Department;

This is useful for data-quality reporting, employee analysis, customer segmentation, and identifying missing business classifications.

  • NULL values can appear as a group.
  • Rows with NULL are generally grouped together.
  • NULL groups can reveal missing classifications.
  • GROUP BY can be used for data-quality analysis.
  • COALESCE can provide a readable label when needed.
What happens when a GROUP BY column contains NULL?

Rows containing NULL are generally placed into a group representing NULL.

How can you display a label instead of NULL?

You can use COALESCE to replace NULL with a meaningful label.

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