Synonyms
Selection (Relational Algebra)
Definition
Given a relation instance R over set of attributes U and a condition F, the selection σF(R) returns a new relation over U consisting of the set of tuples of R which satisfy F. The condition F is an atom of the form A = B or A = c, where A and B are attributes in U and c is a constant value.
The generalized selection allows more complex conditions: F can be an arbitrary Boolean combination of atoms of the form A = B or A ≠ B or A = c or A ≠ c. Moreover, if a total order is defined on the domain of attributes, more general comparison atoms of the form A α B or A α c are allowed, where α ranges over {=, ≠, <, >, ≤, ≥}.
Key Points
The selection is one of the basic operators of the relational algebra. It operates by “selecting” rows of the input relation. A tuple t over U satisfies the condition A = B if the values of attributes A and B in t are equal. Similarly t satisfies the condition A = c if the value of attribute A in t is c....
This is a preview of subscription content, log in via an institution.
Buying options
Tax calculation will be finalised at checkout
Purchases are for personal use only
Learn about institutional subscriptionsAuthor information
Authors and Affiliations
Corresponding author
Editor information
Editors and Affiliations
Section Editor information
Rights and permissions
Copyright information
© 2018 Springer Science+Business Media, LLC, part of Springer Nature
About this entry
Cite this entry
Sirangelo, C. (2018). Selection. In: Liu, L., Özsu, M.T. (eds) Encyclopedia of Database Systems. Springer, New York, NY. https://doi.org/10.1007/978-1-4614-8265-9_1257
Download citation
DOI: https://doi.org/10.1007/978-1-4614-8265-9_1257
Published:
Publisher Name: Springer, New York, NY
Print ISBN: 978-1-4614-8266-6
Online ISBN: 978-1-4614-8265-9
eBook Packages: Computer ScienceReference Module Computer Science and Engineering