Encyclopedia of Database Systems

2018 Edition
| Editors: Ling Liu, M. Tamer Özsu

Membership Query

  • Mirella M. Moro
Reference work entry
DOI: https://doi.org/10.1007/978-1-4614-8265-9_754

Synonyms

Equality query; Equality selection

Definition

Consider a relation R whose schema contains some attribute A taking values over a domain D. A membership query retrieves all tuples in R with A = x (xD).

Key Points

A membership query effectively checks membership in a set (relation). As such, it can be implemented using either a hash-based index (built on the attribute(s) involved in the query) or a B+-tree. If a hashing scheme is used, each indexed value is placed on an appropriate hash bucket. Then all records that satisfy A = x are located on the bucket responsible for value x. If A is a numeric attribute (and can thus be indexed using an order-preserving access method like a B+-tree), the membership query is a special case of a range query where the range interval [low, high] is reduced to a single value (low = high = x).

Cross-References

Copyright information

© Springer Science+Business Media, LLC, part of Springer Nature 2018

Authors and Affiliations

  1. 1.Departamento de Ciencia da ComputaçaoUniversidade Federal de Minas Gerais – UFMGBelo HorizonteBrazil

Section editors and affiliations

  • Leonid Libkin
    • 1
  1. 1.School of InformaticsUniversity of EdinburghEdinburghUK