The authors investigate the problem of inferring join queries from user interactions. The user is presented with a set of candidate tuples and is asked to label them as positive or negative depending on whether or not she would like the tuples as part of the join result. The goal is to quickly infer an arbitrary n-ary join predicate across two relations by keeping the number of user interactions as minimal as possible. They assume no prior knowledge of the integrity constraints between the involved relations. This kind of scenario occurs in several application settings, such as data integration, reverse engineering of database queries, and constraint inference.