| 1 | What are common mistakes developers make when writing subqueries that can lead to incorrect results or poor performance? SQL Server › Subqueries | SQL Server | Subqueries | Intermediate |
| 2 | What is a subquery in SQL Server, and how is it typically used within a larger query? SQL Server › Subqueries | SQL Server | Subqueries | Beginner |
| 3 | What is the difference between a correlated and a non correlated subquery? SQL Server › Subqueries | SQL Server | Subqueries | Beginner |
| 4 | What is the difference between using EXISTS and IN when checking for the presence of related data with a subquery? SQL Server › Subqueries | SQL Server | Subqueries | Intermediate |
| 5 | How do you use a subquery within the SELECT list to calculate a related aggregate value alongside each row of the outer query? SQL Server › Subqueries | SQL Server | Subqueries | Intermediate |
| 6 | How would you rewrite a slow correlated subquery as an equivalent, potentially faster JOIN based query? SQL Server › Subqueries | SQL Server | Subqueries | Advanced |
| 7 | How does the SQL Server query optimizer typically handle and potentially transform a subquery internally when generating an execution plan? SQL Server › Subqueries | SQL Server | Subqueries | Advanced |
| 8 | What is a common table expression, and why would you use one instead of a subquery? SQL Server › Common Table Expressions (CTEs) | SQL Server | Common Table Expressions (CTEs) | Beginner |
| 9 | How do you define multiple common table expressions within a single query? SQL Server › Common Table Expressions (CTEs) | SQL Server | Common Table Expressions (CTEs) | Beginner |
| 10 | What is the difference between a LEFT JOIN and a RIGHT JOIN? SQL Server › Joins | SQL Server | Joins | Beginner |
| 11 | What is the difference between the JSON_VALUE and JSON_QUERY functions? SQL Server › JSON Support in SQL Server | SQL Server | JSON Support in SQL Server | Beginner |
| 12 | How do you filter the results of a grouped query based on an aggregated value, such as only showing customers who spent more than a certain amount? SQL Server › Aggregate Functions & GROUP BY | SQL Server | Aggregate Functions & GROUP BY | Intermediate |
| 13 | What is a recursive common table expression, and what kind of problems is it commonly used to solve? SQL Server › Common Table Expressions (CTEs) | SQL Server | Common Table Expressions (CTEs) | Intermediate |
| 14 | How do you find rows that exist in one table but have no matching row in another table using a join? SQL Server › Joins | SQL Server | Joins | Intermediate |
| 15 | How do you convert a JSON array stored in a column into a relational table format that can be queried like normal rows? SQL Server › JSON Support in SQL Server | SQL Server | JSON Support in SQL Server | Intermediate |
| 16 | Can a common table expression be used inside an UPDATE, DELETE, or MERGE statement, and how does that work? SQL Server › Common Table Expressions (CTEs) | SQL Server | Common Table Expressions (CTEs) | Advanced |