How does the index mechanism accelerate query execution in SQL databases?

Indexes in SQL databases work as pointers to data in a table, allowing the DBMS to quickly find the needed rows without scanning all records. Essentially, an index is a data structure (for example, a B-tree) that stores the values of key columns and references to the corresponding rows.

When a query with a search condition on an indexed column is executed, the DBMS refers to the index to quickly determine where the needed data is located, instead of sequentially scanning the entire table. This significantly reduces query execution time, especially with large volumes of data.

Example: if you have a user table with millions of records and an index on the "email" column, searching for a user by email will be very fast thanks to the index.