Practice sets of sql and MongoDB.
- Jupyter notebook, import sqlite
- Sql Zoo: https://sqlzoo.net/wiki/SELECT_names
- Oracle llive: https://livesql.oracle.com/apex/livesql/file/tutorial_D39T3OXOCOQ3WK9EWZ5JTJA.html
- Sql Fiddle: http://sqlfiddle.com/#!9/c4c1e3/1