What is an index in database?

Oracle includes numerous data structures to improve the speed of Oracle SQL queries. Oracle includes many new indexing algorithms that dramatically increase the speed with which Oracle queries are serviced like b-tree index, bitmap indexes, function-based indexes, and index-only tables (IOTs

Oracle uses indexes to avoid the need for large-table, full-table scans and disk sorts, which are required when the SQL optimizer cannot find an efficient way to service the SQL query. I begin our look at Oracle indexing with a review of standard Oracle b-tree index methodologies.