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Encyclopedia of Database Systems pp 1–2Cite as

Sort-Merge Join

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Synonyms

Merge join

Definition

The sort-merge join is a common join algorithm in database systems using sorting. The join predicate needs to be an equality join predicate. The algorithm sorts both relations on the join attribute and then merges the sorted relations by scanning them sequentially and looking for qualifying tuples.

Key Points

The sorting step groups all tuples with the same value in the join attribute together. Such groups are sorted based on the value in the join attribute so that it is easy to locate groups from the two relations with the same attribute value. Sorting operation can be fairly expensive. If the size of the relation is larger than the available memory, external sorting algorithm is required. However, if one input relation is already clustered (sorted) on the join attribute, sorting can be completely avoided. That is why the sort-merge join looks attractive if any of the input relations is sorted on the join attribute.

The merging step starts with scanning...

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Recommended Reading

  1. Mishra P, Eich MH. Join processing in relational databases. ACM Comput Surv. 1992;24(1):63–113.

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Author information

Authors and Affiliations

  1. Alibaba Group, Hangzhou, China

    Jingren Zhou

Authors
  1. Jingren Zhou
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Corresponding author

Correspondence to Jingren Zhou .

Editor information

Editors and Affiliations

  1. Georgia Institute of Technology College of Computing, Atlanta, Georgia, USA

    Ling Liu

  2. University of Waterloo School of Computer Science, Waterloo, Ontario, Canada

    M. Tamer Özsu

Section Editor information

  1. Department of Computer Science and Engineering, University of Ioannina, P.O. Box 1186, 45110, Ioannina, Greece

    Evaggelia Pitoura

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Zhou, J. (2017). Sort-Merge Join. In: Liu, L., Özsu, M. (eds) Encyclopedia of Database Systems. Springer, New York, NY. https://doi.org/10.1007/978-1-4899-7993-3_867-2

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  • DOI: https://doi.org/10.1007/978-1-4899-7993-3_867-2

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  • Publisher Name: Springer, New York, NY

  • Print ISBN: 978-1-4899-7993-3

  • Online ISBN: 978-1-4899-7993-3

  • eBook Packages: Springer Reference Computer SciencesReference Module Computer Science and Engineering

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