The SQL Tutor is a tutoring system based on constraint-based modeling. Over 500 constraints are used.
Only the SELECT statement is used in SQL Tutor, which means that SQL Tutor can only be used to learn about queries, not updates. That is no serious restriction as the SELECT statement is needed most.
Users can indicate their initial knowledge level.
As the user learns the system keeps track of which clause (select, from, where, group by, having and order by) the user knows least, and suggests exercises that trains that clause.
SQL Tutor may sometimes be available over the Web, but the site may also be down. It is not a fully supported service.
Note for lecture: perform a short SQL Tutor demo!