The HAVING clause is the final filter in your query logic. It allows you to refine your summaries and extract only the most relevant buckets.
1The Aggregate Filter
Since aggregate functions calculate a single value for a group, you need a way to filter based on that value. HAVING AVG(price) > 100 allows you to isolate high-value categories instantly.
2Optimization Logic
Whenever possible, filter your data using WHERE. Reducing the number of rows BEFORE the database has to group and calculate them is much more efficient than filtering the groups AFTERWARDS with HAVING.
3The Duplicate Hunter
HAVING is the ultimate tool for data cleaning. By grouping by a unique field (like an ID or email) and checking HAVING COUNT(*) > 1, you can identify and resolve data integrity issues in seconds.
