JOIN with Aggregation

How can we count employees in each department?

Intermediate⏱ 3 Minutes⭐ 950 XP

🤔 THE QUESTION

How can we count employees in each department?

💡 WHAT IS IT?

Combining LEFT JOIN with GROUP BY aggregates child records against parent dimensions accurately.

🎯 WHAT IS IT USED FOR?

Department headcounts including 0-employee divisions, customer order counts.

💻 EXAMPLE

SELECT d.department_name, COUNT(e.employee_id) AS employee_count
FROM departments d
LEFT JOIN employees e
ON d.department_id = e.department_id
GROUP BY d.department_name;

🎯 Mission Objectives

Practice typing production-grade SQL code for JOIN with Aggregation.

✓ JOIN + GROUP BY
✓ Parent-child aggregation
✓ COUNT on child PK
✓ Department summaries

🚀 Start Mission

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