The SQL sandboxes listed here are a great way to practice your SQL skills and practice querying against a live database.
The interactivity is the killer feature. The sits listed here present guided exercises along with a window to execute SQL and verify your results. They’re perfect for someone who understands the syntax of SQL and next wants to practice solving real problems.
SQL Server
https://sqltest.net/ (Also supports Oracle and MySQL)
http://sqlfiddle.com/ (Also supports Oracle, PostgreSQL, MySQL and SQLite)
Oracle
https://livesql.oracle.com/apex/f?p=590:1000
PostgreSQL
https://dbfiddle.uk/?rdbms=postgres_12
MySQL
https://www.db-fiddle.com/ (also supports PostgreSQL and SQLite)
Other
https://www.w3schools.com/sql/trysql.asp?filename=trysql_select_all
