Self-correcting test bank for SQL basics

Learning SQL needs a lot of practice. Because of the richness of this language it is quite difficult to check and correct these practice exercises. Until now we gave the possibility to our students to upload their solutions into the Moodle and with large workforce, we gave them feedback. My new solution is a flipped method. Students do not upload their solutions in SQL but only answer a question in connection with the result. For example: how many rows are there in the result or what is the name in the first row. It is important to have a sample database with very diversified data so different logically wrong solutions should lead to different wrong answers. The practical quiz in the Moodle will give an immediate feedback including the possible reason for the wrong answer. We can build the database analyzing the typical wrong solutions uploaded by the students in the previous year. We have to deal with the logical errors only because the DBMS checks the syntactics during the work. This test bank will help the students with immediate feedback during their practice but will not be proper for examinations because the correct answers can be guessed in other ways as well.