LeetCode Database Problems
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LeetCode's database section collects several hundred SQL exercises graded by difficulty, run against sample schemas in the browser. Working through them builds fluency with joins, aggregation, window functions, and the query patterns interviewers ask about.
More resources on SQL
Relational Database
Master SQL database concepts with freeCodeCamp's interactive Relational Database course. Build practical projects and gain valuable skills!
SQL in 10 Minutes, Sams Teach Yourself
Ben Forta's short lessons cover the core of standard SQL: SELECT, filtering, joins, subqueries, views, and stored procedures, with examples for several database engines. Finishing gives you working query skills without database-administration detail.
w3schools.com/sql
W3Schools SQL offers a beginner-friendly, interactive guide to SQL, with tutorials and reference covering core SQL commands, clauses, joins, functions, and data manipulation. It includes runnable examples and a “Try it Yourself” editor to practice directly in the browser.
use-the-index-luke.com
A practical guide to database indexing and query optimization, offering clear explanations of how indexes work, how to design them, and tutorials with SQL examples across major relational databases.
sqlzoo.net
SQLZoo.net is an interactive SQL learning resource offering free tutorials and hands-on practice with live databases. It provides step-by-step lessons and coding exercises on SQL topics (SELECT, JOIN, aggregation, etc.) with immediate feedback.
SQL Tutorial
Learn SQL with Mode's free tutorial! Master database querying and analysis with hands-on lessons from the Mode Team.