HAVING and Grouping Pitfalls

HAVING and Grouping Pitfalls

Now that we've covered SQL Aggregate Functions and Grouping in SQL, we're ready for the clause that makes grouped queries interview-ready: HAVING.

GROUP BY creates summary rows. HAVING filters those summary rows.

That distinction matters because many SQL interview questions sound like this:

• "Find customers with more than 3 orders."
• "Show countries whose average order value is above 100."
• "Return products bought by at least 2 distinct users."

These cannot be solved with WHERE alone, because WHERE filters individual rows before aggregation. HAVING filters groups after aggregation.

In this lesson, we'll focus on the mistakes that cause wrong answers even when the query runs.