Part 53: Grouping Data with the GROUP BY Clause

GROUP BY groups rows that share identical values in specified columns, allowing aggregate calculations per group.

1. Basic Syntax

SELECT 
  department,
  COUNT(*) AS employee_count,
  ROUND(AVG(salary), 2) AS average_salary
FROM employees
GROUP BY department;

The Golden Rule of GROUP BY: Any column in the SELECT list that is not inside an aggregate function must appear in the GROUP BY clause!

Key Takeaways

• GROUP BY organizes rows into summary buckets.
• All non-aggregated select columns must be declared in GROUP BY.

In Part 54, we explore Filtering Aggregations with the HAVING Clause (HAVING vs WHERE)!