Often, individual data rows are less informative than summarized information derived from them. After retrieving, filtering, and sorting data, the next step frequently involves calculating summary statistics across groups of rows. This chapter introduces SQL aggregate functions, the tools used to perform these calculations.

You will learn how to:

• Use common aggregate functions like COUNT, SUM, AVG, MIN, and MAX to calculate totals, averages, and find boundary values within your data.
• Group rows that share common characteristics using the GROUP BY clause, allowing aggregates to be calculated for each distinct group. For example, calculating the average order value $AVG(order\_total)$ per customer.
• Filter these grouped results based on aggregate values using the HAVING clause, which operates after the aggregation has occurred.