Introduction

In the previous chapters, we saw that the WHERE clause can be used to filter SQL query result sets in an efficient, almost intuitive way. For example, say we want to identify the total number of executives in a department, or we want the total number of dependents who are covered by a medical claim. In such cases, more than the details, we are looking for a single calculated value. For such cases, where we need calculated results based on database rows, we use SQL aggregate functions. They can also be used to calculate values across subsets of query result rows. We will also look at advanced clauses, such as the GROUP BY and the HAVING clauses, and see how they can help us to fine-tune our results.