相关疑难解决方法(0)

我以为我知道如何使用JOIN,JPQL但显然不是.谁能帮我？

select b.fname, b.lname from Users b JOIN Groups c where c.groupName = :groupName

这给了我例外

org.eclipse.persistence.exceptions.JPQLException
Exception Description: Syntax error parsing the query
Internal Exception: org.eclipse.persistence.internal.libraries.antlr.runtime.EarlyExitException

Users与...有OneToMany关系Groups.

Users.java

@Entity
public class Users implements Serializable{

    @OneToMany(mappedBy="user", cascade=CascadeType.ALL)
    List<Groups> groups = null;
}

Groups.java

@Entity
public class Groups implements Serializable {
    @ManyToOne
    @JoinColumn(name="USERID")
    private Users user;
}

我的第二个问题是让这个查询返回一个唯一的结果,如果我这样做

String temp = (String) em.createNamedQuery("***")
    .setParameter("groupName", groupName)
    .getSingleResult();

***代表上面的查询名称.所以确实fname与lname内部连接在一起temp或者我拿到List<String> …