So far, you have learned to write simple queries that include filtering and ordering. You can also work with expressions built with operators and functions. Chapters 5 and 6 taught you how to write queries with multiple tables so that the data makes sense in applications and reports. Now it’s time to learn about a special type of query, aggregate queries, used to group and summarize data. You may find that writing aggregate queries is more challenging than the other queries you have learned so far, but by taking a step-by-step approach, you will see that they are not difficult to write at all. Be sure to take the time to understand the examples and complete all the exercises before moving on to the next section.