Projection Pushing Revisited

The join operation, which combines tuples from multiple relations, is the most fundamental and, typically, the most expensive operation in database queries. The standard approach to join-query optimization is cost based, which requires developing a cost model, assigning an estimated cost to each queryprocessing plan, and searching in the space of all plans for a plan of minimal cost. Two other approaches can be found in the database-theory literature. The first approach, initially proposed by Chandra and Merlin, focused on minimizing the number of joins rather then on selecting an optimal join order. Unfortunately, this approach requires a homomorphism test, which itself is NP-complete, and has not been pursued in practical query processing. The second, more recent, approach focuses on structural properties of the query in order to find a project-join order that will minimize the size of intermediate results during query evaluation. For example, it is known that for Boolean project-joi...

• Type: Conference
• Year: 2004
• Where: EDBT
• Authors: Benjamin J. McMahan, Guoqiang Pan, Patrick Porter, Moshe Y. Vardi
• Keywords: Database, EDBT 2004, Optimal Join Order, Practical Query Processing, Query Execution Time