https://docs.google.com/presentation/d/15TSfpDc_vESaL_6TST6Df8mHpg_7p7N5ttUrbBV5U9w/edit?usp=sharing
http://theteacher.info/websites/gcse_comp/WebPages/A451_CompSys/215_Databases/RelationalDB/f/f.html
https://www.teachcomputing.net/igcse/cambridge/databases.php
http://www.teach-ict.com/gcse_computing/ocr/databases/concepts/home_db_concepts.htm
QUIZZES
https://www.computerscience.gcse.guru/quiz/database-queries
https://www.computerscience.gcse.guru/quiz/primary-key