With data in different systems, in different formats, and accessed via different tools, we need a lingua franca for data. Not all tools speak SQL, and data cannot be moved into a single convenient location. Relational algebra underpins SQL and many other DB languages. It is also perfect for optimizing, caching and mediating. Apache Calcite (formerly Optiq) is a framework for building and optimizing expressions in relational algebra. We show how to write queries, optimize queries using rewrite rules, and write adapters for back-end systems. We also show to configure Calcite to materialize queries, so your interactive analytics are effectively running against a fast in-memory database.