Theory: Yes, We Need It!
Henrietta Dombrovskaya, Boris Asenovich Novikov, Anna Bailliekova · Apress eBooks · 2021
The chapter starts with overview of query processing performed in the database engine, including parsing, rewriting, optimization, and execution steps, followed by discussion of the optimization and execution steps. It further explain basic relational operations: filter, project, and join, and their relationships with logical operations needed for representation of declarative queries formalated in the SQL query language. Finally, it describes how logical operations are mapped to the implementations needed for execution of a query.