We use analytics and advertising cookies to understand how the site is used and whether our ads on Facebook and Instagram work. They are set only if you accept. See our Privacy Policy for details.
Set operations combine whole result sets vertically: UNION stacks and de-duplicates, UNION ALL stacks and keeps duplicates, and EXCEPT subtracts one set from another. Interviews use them to test whether you know the de-duplication semantics (UNION vs UNION ALL is a classic follow-up) and to solve "in this set but not that one" problems without a join. They come up less often than joins, but when they do, the clean answer is short.
2 problems across 2 schemas · Premium. Each runs your query in an isolated SQLite sandbox with instant, graded feedback.
A quick data question to warm up before you write SQL. No signup needed.
Product data arrives in three normalised source tables: product, subcategory and category. The reporting model needs a single product dimension, and a product's category history must be kept when it changes. How should the data be prepared?
Keep the syntax at your fingertips with the free SQL quick references, then come back and solve.