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SQL Fundamentals — Query Any Database
Learn to ask questions of your data with SQL queries.
SPACED REPETITION · 387 practice questions
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THE NEXT SMALL STEP
Your lessons
Explore a topic, then put your memory to work.
SELECT Basics — Asking Questions
Master the fundamentals of SQL queries: SELECT, FROM, WHERE, filtering, pattern matching, NULL handling, sorting, and limiting results.
Aggregations — Summarizing Data
Learn to summarize and analyze data using COUNT, SUM, AVG, MIN, MAX, GROUP BY, and HAVING. Master the difference between WHERE and HAVING for powerful data analysis.
JOINs — Combining Tables
Learn how to combine data from multiple tables using INNER JOIN, LEFT JOIN, RIGHT JOIN, and FULL JOIN. Understand why databases split data across tables and how to bring it back...
Subqueries — Queries Inside Queries
Master nested queries, correlated subqueries, EXISTS, IN, and learn when to use subqueries versus joins for complex data retrieval.
Data Modification — INSERT, UPDATE, DELETE
Learn to add, modify, and delete data safely. Master INSERT, UPDATE, DELETE statements with proper conditions, RETURNING clause, and transaction basics.
Table Design — CREATE and ALTER
Design robust database tables with proper data types, constraints, and indexes. Learn to create, modify, and optimize table structures.
Advanced Queries — Window Functions
Master window functions for sophisticated data analysis: ROW_NUMBER, RANK, DENSE_RANK, running totals, moving averages, LAG and LEAD. Level up your SQL analytics.
Performance & Best Practices
Master SQL optimization: reading EXPLAIN plans, index strategies, avoiding N+1 queries, and writing maintainable code.
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