Sams Teach Yourself SQL in 10 Minutes, Second Edition

Summary

In Lesson 9, “Summarizing Data,” you learned how to use the SQL aggregate functions to perform summary calculations on your data. In this lesson, you learned how to use the GROUP BY clause to perform these calculations on groups of data, returning results for each group. You saw how to use the HAVING clause to filter specific groups. You also learned the difference between ORDER BY and GROUP BY and between WHERE and HAVING.