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2. How to learn SQL: These are the best online courses

   www.aol.com/learn-sql-best-online-courses...

   SQL is used to communicate with databases. Skip to main content. Sign in. Mail. 24/7 Help. For premium support please call: 800-290-4726 more ways to reach us. Mail. Sign in ...

3. Codecademy - Wikipedia

   en.wikipedia.org/wiki/Codecademy

   Codecademy is an American online interactive platform that offers free coding classes in 13 different programming languages including Python, Java, Go, JavaScript, Ruby, SQL, C++, C#, Lua, and Swift, as well as markup languages HTML and CSS.

4. Exercism - Wikipedia

   en.wikipedia.org/wiki/Exercism

   Exercism is an online, open-source, free coding platform that offers code practice and mentorship [4] on 74 different programming languages. [ 3 ] [ 5 ] History

5. Comparison of online source code playgrounds - Wikipedia

   en.wikipedia.org/wiki/Comparison_of_online...

   Free & Paid No No No Yes MySQL, PostgreSQL, SQLite dbfiddle [an] Free No No No Yes Db2, Firebird, MariaDB, MySQL, Node.js, Oracle, Postgres, SQL Server, SQLite, YugabyteDB ExtendsClass [ao] Free Yes No No Yes MySQL, SQLite (SQL.js) PhpFiddle [ap] Free Yes No No Yes MySQL, SQLite runnable [aj] Free Yes Yes Yes No SQL Fiddle [aq] Free No No No Yes

6. SQL - Wikipedia

   en.wikipedia.org/wiki/SQL

   SQL was initially developed at IBM by Donald D. Chamberlin and Raymond F. Boyce after learning about the relational model from Edgar F. Codd [12] in the early 1970s. [13] This version, initially called SEQUEL (Structured English Query Language), was designed to manipulate and retrieve data stored in IBM's original quasirelational database management system, System R, which a group at IBM San ...

7. Relational model - Wikipedia

   en.wikipedia.org/wiki/Relational_model

   A table in a SQL database schema corresponds to a predicate variable; the contents of a table to a relation; key constraints, other constraints, and SQL queries correspond to predicates. However, SQL databases deviate from the relational model in many details , and Codd fiercely argued against deviations that compromise the original principles.