Add SQL cheatsheet (#5623)

* Update free-programming-cheatsheets.md

* Update free-programming-cheatsheets.md

* Update free-programming-cheatsheets.md

more/free-programming-cheatsheets.md

@@ -172,3 +172,4 @@
 
 * [MySQL Cheatsheet](https://s3-us-west-2.amazonaws.com/dbshostedfiles/dbs/sql_cheat_sheet_mysql.pdf) - Database Star (PDF)
 * [PostgreSQL Cheatsheet](https://s3-us-west-2.amazonaws.com/dbshostedfiles/dbs/sql_cheat_sheet_pgsql.pdf) - Database Star (PDF)
+* [SQL Cheatsheet](https://www.codecademy.com/learn/learn-sql/modules/learn-sql-manipulation/cheatsheet) - Codecademy (SQL)