Advanced Database Management System - Tutorials and Notes: Primary index dense index

Saturday, 21 November 2015

Primary index dense index

Primary index - Dense index / What is dense index? / Define Dense index / Dense index example

Dense Index

Index entry appears for every search key value in the record file (data file). In other words, “one entry in the index file for every record that is stored in the data file”.
For example, consider the figure (primary index) given below. You may find all the register numbers that are part of the data file as search key entries in the index file. This type of primary index is called as dense index. 

Primary index - Dense index

Points to remember about dense indexes:

  • Every value of the key attribute of the data file has a representative entry in the appropriate dense index file. Hence the number of entries in the index file is equal to the number of records in the data file.

  • The index maintains the key values in the same order as in the data file.

  • It supports point queries, and range queries (if the look up attribute is the indexed attribute).

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