What methods can be used to implement indexing in a database?

Database indexing is a way to speed up data search and sorting. The main methods of implementing indexing are:

1. B-trees (B-Tree) — the most common type of index, suitable for range searches and exact lookups.
2. Hash indexes — effective for exact key searches but do not support range searches.
3. Full-text indexes — used for quick text searches.
4. Composite key indexes — index multiple columns simultaneously.

In Java, when working with databases (e.g., via JDBC or ORM), indexing is created at the DBMS level using SQL commands:

CREATE INDEX idx_name ON table_name(column_name);

Or using annotations in ORM, for example, in Hibernate:

@Entity
@Table(name = "users", indexes = {
    @Index(name = "idx_username", columnList = "username")
})
public class User {
    // fields
}

Indexes improve query performance but increase the time for inserting and updating data, so they should be used thoughtfully.