What is the role of indexes in a database and how do they help speed up query execution?

Indexes in a database are special data structures that speed up the search and retrieval of data from tables. They work like pointers or contents in a book, allowing you to quickly find the needed records without scanning all rows.

Role of indexes:

• Accelerate the execution of SELECT queries, especially with WHERE, JOIN, ORDER BY conditions.
• Help quickly find data by keys.
• Can improve the performance of sorting and grouping.

Example: if you have a user table with millions of records, an index on the email field will allow you to quickly find a user by email without scanning the entire table.

Example of creating an index in SQL:

CREATE INDEX idx_users_email ON users(email);

After that, the query

SELECT * FROM users WHERE email = 'example@mail.com';

will execute much faster.