What is indexing in relational databases?

Indexing in relational databases is a mechanism for creating special data structures (indexes) that speed up the search and retrieval of data from tables. Indexes act as pointers to table rows, allowing quick access to the required records without scanning all data.

For example, if you have a users table with an email field, creating an index on this field will allow you to quickly find a user by email, significantly speeding up SELECT queries with a WHERE email = 'example@example.com' condition.

Indexes can be of different types: B-trees, hash indexes, etc. However, indexes occupy additional space and slow down insert, update, and delete operations, as the index itself also needs to be updated.