SQL Querying: Handling NULL Values and Unique Constraints

Working with missing or unknown data is one of the most common challenges in database development. This text-only course guides you through the nuances of SQL's three-valued logic, helping you understand how NULL behaves under the hood and how to manage it without errors. You will transition from guessing how NULL values interact with your queries to confidently designing tables and writing precise data retrieval statements. What you'll learn: - Understand the core concept of NULL as an unknown state rather than zero or an empty string - Master three-valued logic (TRUE, FALSE, UNKNOWN) and its impact on WHERE clauses - Implement unique constraints that correctly handle single or multiple NULL entries across different database systems - Apply COALESCE and NULLIF functions to provide fallback defaults and clean up query outputs - Write robust conditional logic using CASE expressions to handle missing data dynamically You will begin with foundational definitions, learning how SQL treats unknown values, before moving into practical query patterns, indexing strategies, and modern database constraints. This course is designed for beginner database administrators, data analysts, and software developers who want to write clean, predictable SQL code. No advanced database experience is required to start. Dive into the text and master database logic today.