What type of information is typically stored within an index in a database?

An index in a database is primarily used to enhance the speed of data retrieval operations on a database table. It functions much like an index in a book, which helps you quickly find the page where a specific topic is discussed. In the context of databases, the index contains references to the locations of data records, allowing the database management system to locate the desired data more efficiently.

When you perform a search or query that involves indexed fields, the database can quickly locate the index entries and, consequently, the actual data records, rather than scanning the entire table. This significantly improves performance, especially in large databases.

The other alternatives do not accurately describe the role of an index. Redundant and irrelevant data goes against the purpose of indexing, while storing complete data entries is the function of the database itself, not the index. Finally, queries for data retrieval are functions executed on the database rather than information stored within the index.