Filtering Groups

Imagine we manage an online store with thousands of products, and we need to identify which product categories have a minimum number of products before launching a special promotion. Or consider creating a sales report where we might want to display only the groups of products where the total sales exceeded $100. We already know how to group data using the GROUP BY clause, but how do we filter those groups? That is where the HAVING clause comes in.

Let’s explore the HAVING clause in SQL. We will go step by step to:

• Use the HAVING clause to filter out entire groups that do not meet certain criteria.

• Understand why WHERE does not work directly on aggregated values and why we need HAVING instead.

• Recognize the difference between filtering individual rows (WHERE) and filtering grouped data (HAVING).

Importance of filtering groups

We often group rows to perform aggregate calculations like COUNT, SUM, AVG, MIN, and MAX. However, sometimes we want only those groups that meet a specific condition, such as having more than a certain number of items or reaching a certain total price. Filtering groups lets us focus on relevant clusters of data for more targeted insights.

The HAVING clause

The HAVING clause is used to filter results after we apply GROUP BY. In SQL, the basic syntax of using the HAVING clause is shown below: