Module Overview

What You’ll Learn

• Write advanced SQL queries
• Reuse query results
• Handle conditional logic
• Combine query results

💡 Why this module matters: Some real questions genuinely can’t be answered with one flat query, “customers who spent more than average,” for instance, needs a query inside a query. This module covers the tools for exactly that.

What’s Covered

• Subqueries and correlated subqueries, a query nested inside another.
• Common Table Expressions (CTEs), naming and reusing a subquery with WITH.
• CASE, conditional logic directly inside a query.
• COALESCE and NULLIF, handling NULL values gracefully.
• EXISTS, ANY, and ALL, existence and comparison checks against a subquery.
• UNION, UNION ALL, INTERSECT, and EXCEPT, combining the results of separate queries.

Hands-On

By the end of this module, you’ll build reporting queries, use CTEs, write conditional queries, and combine datasets from multiple queries into one result.

Next module turns to performance, packaging queries as views, and speeding them up with indexes.