Question

In terms of databases: What are multi level indexes? Why do we need them and are they any good? What are their merits and demerits?

Answer 1

A database multi level indexes are the data structure that optimizes the speed of data collection operations in a database table in terms of storage space and additional storage space to maintain the index database structure. The index is used to quickly search for data without having to search for individual rows in a database table each time you access a database table. Indexes can be created using one or more columns from a database table, providing the foundation for both quick random searches and high-level record retrieval.

An index is a copy of a column of data selected from a table called a database key, or a keyword that can be effectively searched for, and includes a low-level block address of a disk or a direct link to a data row. Some databases extend the power of indexing by allowing developers to create indexes for functions or expressions. For example, an index can be created above (last name) that will only contain uppercase letters of the last name field in the index. Another option that is sometimes supported is the use of partial indexes, where index records are created only for those records that satisfy a specific condition. Another aspect of flexibility is to allow indexing of user-defined functions as well as expressions created by the classification of the functions that come with it.
Most database software includes indexing technology that allows sublinear time search to improve performance because linear search is not effective for large databases.

Assume that the database contains N data entries and one is retrieved based on the value of a field. Simple practice implementation and examine each item according to the test. If there is only one matching item, it can stop when a single item is found, but if there are multiple matches, it must try everything. This means that the number of operations in the average case is O(N) or linear time. Because databases can contain many objects, and because search is a routine operation, it is often desirable to improve performance.