In relational algebra, a selection (sometimes called a restriction in reference to E.F. Codd's 1970 paper and not, contrary to a popular belief, to avoid confusion with SQL's use of SELECT, since Codd's article predates the existence of SQL) is a unary operation that denotes a subset of a relation. A selection is written as or where: * a and b are attribute names * θ is a binary operation in the set * v is a value constant * R is a relation The selection denotes all tuples in R for which θ holds between the a and the b attribute. The selection denotes all tuples in R for which θ holds between the a attribute and the value v. For an example, consider the following tables where the first table gives the relation Person, the second table gives the result of and the third table gives the result of . More formally the semantics of the selection is defined asfollows: The result of the selection is only defined if the attribute names that it mentions are in the heading of the relation that it operates upon. (Wikipedia).
Relational Databases (part 4 of 6)
The essential concepts of relational databases. Part of a larger series teaching programming. Visit codeschool.org
From playlist Relational Databases
Sets might contain an element that can be identified as an identity element under some binary operation. Performing the operation between the identity element and any arbitrary element in the set must result in the arbitrary element. An example is the identity element for the binary opera
From playlist Abstract algebra
Relational Databases (part 1 of 6)
The essential concepts of relational databases. Part of a larger series teaching programming. Visit codeschool.org
From playlist Relational Databases
The elements of a set can be ordered by a relation. Some relation cause proper ordering and some, partial ordering. Have a look at some examples.
From playlist Abstract algebra
The SQL Create Index Statement
This video explains how to use the CREATE INDEX statement of the Structured Query Language (SQL). It is the third in a series about a subset of SQL known as the Data Definition Language (DDL), which can be used to create and modify the table structures within a relational database. It in
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Introduction to Relations and Functions
An introduction to relations and functions. Discussion includes defining, classifying, and examples of relations and functions, as well as five ways to represent relations and functions,
From playlist Algebra 1
Citus Architecture Extending Postgres to Build
Citus is a distributed database that scales out Postgres. By using the extension APIs, Citus distributes your tables across a cluster of machines and parallelizes SQL queires. This talk describes the Citus architecture by focusing on our learnings in distributed systems. http://www.pgconf
From playlist 2016
Hecke Endomorphism Algebras, Stratification, finite groups of Lie type, and ı-quantum algebras
Recorded for UVa Conference Presented by Jie Du (joint work with B. Marshall and L. Scott)
From playlist Pure seminars
Yoshiko Ogata - Classification of Gapped Ground State Phases in Quantum Spin Systems
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From playlist Quantum Encounters Seminar - Quantum Information, Condensed Matter, Quantum Field Theory
O'Reilly Webcast: Nullology: The Zen of Database
Nullology is the study of the empty set. Of course, sets crop up all over the place in the database world; but the question is--and it's a crucial one--what happens if the set under consideration happens to be empty? For example, a relation contains a set of tuples: what about the possibil
From playlist O'Reilly Webcasts
Non-Invertible Symmetries and their Representations
IAS High Energy Theory Seminar Topic: Non-Invertible Symmetries and their Representations Speaker: Sahand Seifnashri Affiliation: Member, School of Natural Sciences, IAS Date: September 16, 2022 In the first half of the talk, I will review the notion of non-invertible symmetries and how
From playlist IAS High Energy Theory Seminar
Piotr Sniady: Representation theory from the random matrix perspective
Talk at the conference "Noncommutative geometry meets topological recursion", August 2021, University of Münster. Abstract: In many cases a representation of a group can be viewed as a "random matrix with non-commutative entries". This viewpoint gives a heuristic explanation for many links
From playlist Noncommutative geometry meets topological recursion 2021
GoGaRuCo 2010 - Arel: The Ruby Relational Algebra Library by: Bryan Helmkamp
Arel (also known as ActiveRelation) is the Ruby relational algebra engine powering ActiveRecord in Rails 3. By replacing string concatenation with an object model to express SQL queries, Arel had a big immediate impact on the ActiveRecord codebase and opens the door for more powerful Objec
From playlist GoGaRuCo 2010
Isomorphisms in abstract algebra
In this video I take a look at an example of a homomorphism that is both onto and one-to-one, i.e both surjective and injection, which makes it a bijection. Such a homomorphism is termed an isomorphism. Through the example, I review the construction of Cayley's tables for integers mod 4
From playlist Abstract algebra