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Chapter 15: Problem 17

Can a nondense index be used in the implementation of an aggregate operator? Why or why not?

Short Answer

Expert verified
No, a nondense index is not optimal for implementing aggregate operators in a database due to the lack of one-to-one correspondence between search keys and index entries, which leads to inefficient retrieval of individual records necessary for aggregate calculations.

Step by step solution

01

Understanding Nondense Index

A nondense index is a type of database index where not all search key values have a corresponding index entry. In a non-dense index, each entry in the index points to a block rather than individual records. This index type can lead to inefficient searches for records because it lacks a one-to-one correspondence between search keys and index entries.
02

Understanding Aggregate Operators

Aggregate operators in databases are functions that take a set of values and return a single, more significant value. Common aggregate functions include COUNT(), SUM(), AVG(), MAX(), MIN(). These operators are frequently used in conjunction with GROUP BY clause in SQL to group data by certain columns and then perform calculations on each group.
03

Assessing the Feasibility

When implementing aggregate operators, it is important to efficiently access all necessary rows. A nondense index is less helpful in this scenario because it does not support efficient retrieval of individual records, which may be required for aggregate calculations. Inspecting a block referenced via a nondense index may result in examining unnecessary records. So, it would be quite ineffective to use a nondense index in the implementation of an aggregate operator.

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