Criando classes domínio

Crie uma classe import.sql e jogue o seed todo lá para deixar salvo e documentado.

User

@NoArgsConstructor
@AllArgsConstructor
@Getter
@Setter
@ToString
public class User {

    private int id;
    private String name;
    private String email;

}

Book

@NoArgsConstructor
@AllArgsConstructor
@Getter
@Setter
@ToString
public class Book {
    
    private Integer id;
    private String name;
    private String description;
    private String author;
    private String category;

}

UserBookLoan

@NoArgsConstructor
@AllArgsConstructor
@Getter
@Setter
@ToString
public class UserBookLoan {

    private User user;
    private Book book;
    private Date loanDate;
}