What is indexing in databases and why is it needed?

Indexing in databases involves creating special data structures (indexes) that speed up the search and sorting of records based on certain table fields. Without indexes, the DBMS must scan all rows (full scan) when executing a query, which slows down performance with large volumes of data.

Indexes allow quick retrieval of needed records, significantly improving the performance of SELECT queries, especially with WHERE, JOIN, and ORDER BY conditions. However, indexes occupy additional space and slow down insert, update, and delete operations because the index structures need to be updated.

Example: if you have a users table with an email field, creating an index on email will allow you to quickly find a user by this address.

CREATE INDEX idx_users_email ON users(email);