What is the primary function of an index in a database?

The primary function of an index in a database is to speed up querying. An index is a data structure that improves the speed of data retrieval operations on a database table at the cost of additional storage space and potentially slower writes and updates. By creating indexes on one or more columns, the database can locate data more efficiently without having to scan the entire table. This is similar to an index in a book, where specific topics can be quickly located rather than searching through every page.

Indexes work by maintaining a sorted order of keys. When a query is performed, the database can use the index to quickly narrow down the search to a specific subset of data, which drastically reduces the time it takes to retrieve results compared to performing a full table scan. This is especially crucial when dealing with large datasets, where the performance impact of querying can be significant.

Other options, such as enhancing data entry speed or increasing data redundancy, do not accurately reflect the role of indexes. While an index might indirectly influence performance during data entry, its primary design is centered around optimizing query performance. The idea of slowing down database transactions or increasing redundancy does not align with the database indexing purpose, which is fundamentally about efficient data retrieval.