Sparse and Dense Indexes
These indexes in principle are the similar as that of indexes used at the back of the book. The key facts of the indexes are:
- They are arranged on the order of the index value (ascending or descending) as per the option of the creator.
- The indexes are logically individual files (just like individual index pages of the book).
- An index is firstly formed for fast access of information.
- The primary index is the index on the ordering field of the data file while a secondary index is the index on any other field, therefore, more useful.
But what are dense and sparse indexes?
Sparse indices are the indices that do not contain all the available values of a field. An index sets the records as per the index values. A sparse index is where the size of the group is one or more, whereas in a dense index the size of the group is 1. In other words a dense index have one index entry for each value of the indexing attributes, while a sparse index also known as non-dense index have few index entires out of the available indexing attribute values. For instance, the primary index on enrolment number is sparse, whereas secondary index on student name is dense.