Synonyms
Non-clustering index
Definition
A tree-based index is called a secondary index if the order which it maintains on the search-key values is not the same as the order of the file which it indexes. For example, consider a relation R with some numeric attribute A taking values over an (ordered) domain D. Assume that relation R is not physically stored on the values of attribute A (i.e., relation R is either stored as a heap – an unordered file, or is ordered on another attribute). Furthermore, assume that a tree-based index (e.g., B+ -tree) has been created on attribute A. Then this index is secondary.
Key Points
Tree-based indices are built on numeric attributes and maintain an order among the indexed search-key values. They are further categorized by whether their search-key ordering is the same with the file’s physical order (if any). Note that a file may or may not be ordered. Ordered is a file whose records are stored in pages according to the order of the values of an...
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Elmasri RA, Shamkant NB. Fundamentals of database systems. 5th ed. Reading: Addisson-Wesley; 2007.
Manolopoulos TY, Tsotras Y, Vassilis J. Advanced database indexing. Dordecht: Kluwer; 1999.
Ramakrishnan R, Gehrke J. Database management systems. 3rd ed. New York: McGraw-Hill; 2003.
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Manolopoulos, Y., Theodoridis, Y., Tsotras, V.J. (2018). Secondary Index. 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_758
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DOI: https://doi.org/10.1007/978-1-4614-8265-9_758
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