Databases

Most database learning starts with SQL. Interactive tutorials such as SQLBolt, Select Star SQL and SQLZoo let you write queries in the browser from the first lesson, and CS50's Introduction to Databases with SQL adds structured lectures and problem sets. Online editors like SQLite Online and SQLFiddle are useful for testing queries.

To understand how databases work internally, the CMU Database Group's Intro to Database Systems and Advanced Database Systems lectures cover storage, indexing, query execution and transactions. Cornell's Database Systems course covers both SQL and NoSQL. The cheat sheets for MySQL, PostgreSQL and standard SQL are useful references during day-to-day work.