SQL

• https://de.wikipedia.org/wiki/SQL

Fiddles

SQL Fiddle

• http://sqlfiddle.com/#!5/7938a/1
• https://github.com/zzzprojects/sqlfiddle3

• https://www.db-fiddle.com/f/kUnajtCwrSZo9iNNTPXEXr/0

Tutorials

• https://sqlbolt.com/
• SQL Zoo