In this project, I am using JPA/Hibernate and I found an interesting annotation called @Index from the javax.persistence package that can help me create an index without writing SQL. However, I don’t know what kind of index the @Index creates, because it does not provide an option for the type of index.

I want to create the index for the username field on the Users table as a hash index for searching, and a tree index for the userAge field on the Users table for the purpose of comparison.

>Solution :

The @Index annotation in JPA/Hibernate is used to create indexes on columns of a database table without writing SQL. However, the @Index annotation does not provide an option to specify the type of index, which means the type of index created is determined by the database provider being used.

@Target({})
@Retention(RUNTIME)
public @interface Index {
    String name() default "";
    String columnList();
    boolean unique() default false;
}

As you can see, only the columnList attribute is mandatory, which we have to define.

One aspect to note here is that the annotation doesn’t support changing the default indexing algorithm

The exact type of index created by the @Index annotation will depend on the database provider and its configuration. Generally, the database provider will choose the most appropriate type of index based on the table schema and the data being indexed.

Here is an example to create an index

@Entity
@Table(indexes = {
  @Index(columnList = "firstName"),
  @Index(name = "fn_index", columnList = "firstName"),
  @Index(name = "mulitIndex1", columnList = "firstName, lastName"),
  @Index(name = "mulitIndex2", columnList = "lastName, firstName"),
  @Index(name = "mulitSortIndex", columnList = "firstName, lastName DESC"),
  @Index(name = "uniqueIndex", columnList = "firstName", unique = true),
  @Index(name = "uniqueMulitIndex", columnList = "firstName, lastName", unique = true)
})
public class Student implements Serializable