What is the main reason behind using an index?

Faster access of data blocks in the table.

The main reason for using an index in PL/SQL (and in databases in general) is to improve the performance of query operations. Indexes provide a quick and efficient way to locate rows in a table based on the values in one or more columns. They act like a roadmap, allowing the database engine to quickly narrow down the search space and retrieve the desired data more efficiently.

By using indexes, you can significantly speed up the execution of SELECT, UPDATE, DELETE, and MERGE statements, as the database engine can quickly locate the rows that match the search criteria without scanning the entire table. However, it’s important to note that while indexes can improve read performance, they may have a slight impact on write operations (such as INSERT, UPDATE, and DELETE), as the indexes also need to be maintained when the underlying data changes.

In summary, the main reason for using an index is to enhance the performance of data retrieval operations in a database by providing a quick and efficient way to locate the desired rows.