Ranked enumeration of join queries with projections

Join query evaluation with ordering is a fundamental data processing task in relational database management systems. SQL and custom graph languages such as Cypher offer this functionality by allowing users to specify the order via ORDER BY clause. In many scenarios, also want see first k results quickly (expressed LIMIT clause), but value of not predetermined user queries are arriving an online fashion. Recent work has made considerable progress identifying optimal algorithms for ranked enumeration join that do contain any projections. paper, we initiate study problem enumerating Our main result shows acyclic query, it possible obtain near-linear (in size database) delay algorithm after only linear time preprocessing step two important ranking functions: sum lexicographic ordering. For practical subset known star queries, show even stronger allows smooth tradeoff between faster answering guarantees using more time. extensible containing cycles unions. We perform comprehensive experimental demonstrate our algorithms, which simple implement, improve up three orders magnitude running over state-of-the-art implemented within open-source RDBMS specialized databases.