How does an index speed up data search by a specific field in a database?

An index in a database is a data structure that speeds up the search for records based on a specific field, similar to a pointer in a book.

Without an index, the database management system (DBMS) must scan all records (full scan) when searching by a field, which takes a lot of time with large volumes of data.

An index stores sorted values of the field and references to the corresponding records. When searching by index, the DBMS quickly finds the needed value using binary search or other algorithms, significantly reducing the number of operations.

For example, if there is an index on the "email" field, searching for a user by email will be fast, even if the table contains millions of records.