Apache Calcite is an open source framework for building databases and data management systems. It includes a SQL parser, an API for building expressions in relational algebra, and a query planning engine. As a framework, Calcite does not store its own data or metadata, but instead allows external data and metadata to be accessed by means of plug-ins.

Several other Apache projects use Calcite.^[3] Hive uses Calcite for cost-based query optimization;^[4] Drill and Kylin use Calcite for SQL parsing and optimization; Samza and Storm use Calcite for streaming SQL. As of August 2016, Apex, Phoenix and Flink have projects under development that use Calcite.