  SQL is a central component of any database course. Despite the small number
of SQL commands, students struggle to practice the concepts. To overcome this
challenge, we developed an intelligent tutoring system (ITS) to guide the
learning process with a small effort by the lecturer. Other systems often give
only basic feedback (correct or incorrect) or require hundreds of instance
specific rules defined by a lecturer. In contrast, our system can provide
individual feedback based on a semi-automatically/intelligent growing pool of
reference solutions, i.e., sensible approaches. Moreover, we introduced the
concept of good and bad reference solutions. The system was developed and
evaluated in three steps based on Design Science research guidelines. The
results of the study demonstrate that providing multiple reference solutions
are useful with the support of harmonization to provide individual and
real-time feedback and thus improve the learning process for students.
