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One concept. Every database.

Every SQL idea is shown side-by-side across the databases you actually use in production — and translated to MongoDB when you leave the relational world.

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PostgreSQL
MySQL
MariaDB
SQL Server
Oracle
Db2
MongoDB

Why this guide is different

Multi-database examples

See the exact syntax for SQL Server, MySQL, PostgreSQL, Oracle, Db2 and MariaDB — dialect differences highlighted, not hidden.

SQL to NoSQL

Understand how a relational query maps to a MongoDB document query, so you can move between paradigms with confidence.

Built for everyone

Structured for translation from day one, with clean semantic markup and structured data for search engines.

Lessons

Work through the fundamentals, one concept at a time.

1What is SQL?Beginner5 minSQL is the language for asking questions of relational databases. Learn what it is, why every major database speaks a dialect of it, and how it differs from NoSQL.
2SELECT: choosing columns and rowsBeginner8 minRetrieve exactly the columns and rows you need with SELECT and WHERE, and see how the same filter is expressed in MongoDB.
3Limiting results: the biggest dialect splitIntermediate7 minReturning just the top N rows is where SQL dialects diverge the most. Compare LIMIT, TOP and FETCH FIRST across every database, plus MongoDB's limit().