Database management systems (DBMS) constitute the backbone of today's information-rich society. A primary reason for the popularity of database systems is their support for declarative queries, typically in the SQL query language. In this programming paradigm, the user only specifies the end objectives, leaving it to the DBMS to automatically identify the optimal execution strategy to achieve these objectives. Declarative specification of queries is also central to parallel query execution in modern big data platforms.
Query processing and optimization have been extensively researched for close to five decades now, and are implemented in all contemporary database systems. Nevertheless, important challenges remain unsolved, and Indian universities have played a visible role in addressing these issues. As exemplars, we highlight recent research contributions on robust query processing, holistic optimization of database applications, and testing strategies for SQL queries and database engines.