SQL Query Development: Learning to Retrieve, Filter, Sort, Combine, and Analyze Data from Relational Databases
Learn to write SQL queries that answer the right question-not just queries that run.
SQL syntax can be learned quickly. The harder skill is knowing how to turn a real-world question into a precise result, choose the right tables, preserve the meaning of the data, handle duplicates and missing values, and verify that the results are actually correct.
SQL Query Development is a practical, reasoning-first guide for learning those skills from the ground up.
Starting with simple SELECT statements, you'll progressively learn how to:
Retrieve exactly the columns and rows you need
Filter data with WHERE, logical conditions, ranges, lists, patterns, and NULL-aware logic
Sort and limit results reliably and build deterministic Top-N queries
Create calculated columns and conditional logic with expressions, CASE, and functions
Summarize data using aggregates, GROUP BY, and HAVING
Combine related tables with INNER, LEFT, RIGHT, FULL, CROSS, and self joins
Use subqueries, EXISTS, derived tables, and common table expressions
Combine result sets with UNION, INTERSECT, and EXCEPT
Perform practical sales, customer, inventory, staffing, and data-quality analysis
Diagnose duplicate rows, missing rows, incorrect filters, NULL problems, and faulty calculations
Develop more readable, maintainable queries while building basic performance and index awareness
Translate requirements into queries and validate results with deliberate test cases
Rather than teaching SQL as a collection of isolated commands, this book develops a repeatable query-building process: define the question, determine what one row should represent, identify the required tables and relationships, build in small steps, test edge cases, and validate the result.
You'll work primarily with the fictional Harbor Retail database, with customers, products, orders, order items, employees, and departments. Exercises and increasingly challenging scenarios give you opportunities to predict results, investigate unexpected output, debug queries, and practice professional query development.
The book also highlights important differences among PostgreSQL, MySQL, SQL Server, Oracle Database, and SQLite so you can understand which SQL concepts transfer across platforms and where syntax may differ.
Whether you're learning SQL for the first time, strengthening your database skills, or looking for a structured way to improve how you write and review queries, SQL Query Development focuses on the skill that matters most:
understanding why a query produces the result it produces-and knowing whether that result deserves to be trusted.
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