Parallel execution of SQL queries against large databases offers a solution to the problem of reducing query response. This book addresses the related optimization problem: Given an SQL query, find the plan that delivers the result in minimal time. The author presents and analyzes new theoretical findings and efficient algorithms pertaining to parallel operation at a practical level of granularity relevant to database system operations. The optimization results balance the advantages and costs of parallel execution of SQL queries. The techniques presented are applicable to modern system configurations, where computation is performed on pipelining-capable workstations operating in parallel, and can be used to construct SQL compilers able to exploit parallel machines effectively.