This case introduces students to relational databases and the basics of collaborative filtering, a popular recommendation system technique. The case points to a dataset shared by GroupLens, a research group developing algorithms that supply movie recommendations through a website called MovieLens. SQL queries provided in the case propose a collaborative filtering strategy for generating simple recommendations with a small degree of personalization. The basic method offered in the case opens the door for students to improve the supplied queries or develop a more elaborate algorithm altogether for generating recommendations.