Lecture

Relational Algebra Equivalences: Optimization Techniques

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In course

CS-422: Database systems

This course is intended for students who want to understand modern large-scale data analysis systems and database systems. It covers a wide range of topics and technologies, and will prepare students to be able to build such systems as well as read and und ...

Description

This lecture covers the key concept of equivalences in relational algebra expressions, allowing for optimization by generating the same set of tuples more efficiently. Various equivalences involving selections, projections, and joins are discussed, along with examples demonstrating their application. The lecture also explores the impact of different join orders, the commutativity of selections and projections, and the benefits of pushing down projections. Additionally, it delves into naive and educated approaches to query optimization, highlighting the significant performance differences. The instructor emphasizes the importance of using joins instead of cross products and pushing down projections to achieve efficient query execution.

Instructor

Anastasia Ailamaki

Expertise Database management systems, scientific applications, computer architecture Teaching & PhD PhD Students Hamish Nicholson, Anna Herlihy, Yi Jiang, Eleni Zapridou, Georgiy Konstantinovich Lebedev, Ioanna Tsakalidou Past EPFL PhD Students Farhan Tauheed, Radu Ioan Stoica, Manos Athanassoulis, Pinar Tözün, Adrian Daniel Popescu, Ioannis Alagiannis, Renata Borovica-Gajic, Danica Porobic, Iraklis Psaroudakis, Manos Karpathiotakis, Matthaios Alexandros Olma, Mirjana Pavlovic, Eleni Tzirita Zacharatou,

Official source

Ontological neighbourhood

Computer engineering

Databases: Relational databases

Related concepts (31)

Query plan

A query plan (or query execution plan) is a sequence of steps used to access data in a SQL relational database management system. This is a specific case of the relational model concept of access plans. Since SQL is declarative, there are typically many alternative ways to execute a given query, with widely varying performance. When a query is submitted to the database, the query optimizer evaluates some of the different, correct possible plans for executing the query and returns what it considers the best option.

Relational database

A relational database is a (most commonly digital) database based on the relational model of data, as proposed by E. F. Codd in 1970. A system used to maintain relational databases is a relational database management system (RDBMS). Many relational database systems are equipped with the option of using SQL (Structured Query Language) for querying and updating the database. The term "relational database" was first defined by E. F. Codd at IBM in 1970. Codd introduced the term in his research paper "A Relational Model of Data for Large Shared Data Banks".

Foreign key

A foreign key is a set of attributes in a table that refers to the primary key of another table. The foreign key links these two tables. Another way to put it: In the context of relational databases, a foreign key is a set of attributes subject to a certain kind of inclusion dependency constraints, specifically a constraint that the tuples consisting of the foreign key attributes in one relation, R, must also exist in some other (not necessarily distinct) relation, S, and furthermore that those attributes must also be a candidate key in S.

Relational model

The relational model (RM) is an approach to managing data using a structure and language consistent with first-order predicate logic, first described in 1969 by English computer scientist Edgar F. Codd, where all data is represented in terms of tuples, grouped into relations. A database organized in terms of the relational model is a relational database.

Relational calculus

The relational calculus consists of two calculi, the tuple relational calculus and the domain relational calculus, that is part of the relational model for databases and provide a declarative way to specify database queries. The raison d'être of relational calculus is the formalization of query optimization, which is finding more efficient manners to execute the same query in a database.

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