HQL查询语言的作用是什么

本篇文章为大家展示了HQL查询语言的作用是什么，内容简明扼要并且容易理解，绝对能使你眼前一亮，通过这篇文章的详细介绍希望你能有所收获。

1.获取Hibernate Session对象
2.编写HQL语句
3.以HQL语句作为参数，调用Session的createQuery方法创建查询对象
4.如果HQL语句包含参数，则调用Query的setXxx方法为参数赋值
5.调用Query独享的list()或uniqueResult()方法返回查询结果列表

简单的例子：

复制代码 代码如下:

@SuppressWarnings("deprecation")
public class HibernateUtil {

    private static final SessionFactory sessionFactory;

    static {
        sessionFactory = new AnnotationConfiguration().configure().buildSessionFactory();
    }

    public static Session getOpenSession() {
        return sessionFactory.openSession();
    }

    public static Session getCurrentSession() {
        return sessionFactory.getCurrentSession();
    }
}
@Entity
public class Employee {

    private Integer id;
    private String name;
    private Integer age;

    @Id
    @GeneratedValue
    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    @Basic
    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @Basic
    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

    public String toString() {
        return "id:" + id + "   " + "name:" + name +  "   " + "age:" + age;
    }
}
@SuppressWarnings("all")
public class HQLDemo {

    @Test
    public void testHQL() {
        Session session = HibernateUtil.getOpenSession();
        List<Employee> employeeList = session.createQuery("from Employee as e").list();
        for(Employee e : employeeList)
            System.out.println(e);
    }

    @Test
    public void testHQLHasParameter() {
        Session session = HibernateUtil.getOpenSession();
        List<Employee> employeeList = session.createQuery("from Employee as e where e.name = :personName").setString("personName", "xujianguo").list();
        for(Employee e : employeeList)
            System.out.println(e);
    }
}

HQL查询的from子句：

from是最简单的HQL语句，也是最基本的HQL语句，from关键字后紧跟持久化类的类名，如：

from Employee表名从Employee类中选出全部的实例

不过我们常用的是这样做：

from employee as e这个e就是Employee的别名，也就是实例名，推荐这么写。

　　HQL查询的select子句：

　　select子句用于选择指定的属性或直接选择某个实体，当然select选择的属性必须是from后持久化类包含的属性，如：

select e.name from Employee as e　　select可以选择任意属性，即不仅可以选择持久化类的直接属性，还可以选择组件属性包含的属性，如：

select e.name.firstName from Employee as eHQL查询的聚集函数：

　　聚集函数：　　

　　　　avg：计算属性的平均值

　　　　count：统计选择对象的数量

　　　　max：统计属性值的最大值

　　　　min：统计属性值的最小值

　　　　sum：计算属性值的总和

如：

复制代码 代码如下:

select count(*) from Employee as e    @Test
    public void testHQLFunction() {
        Session session = HibernateUtil.getOpenSession();
        System.out.println(session.createQuery("select count(*) from Employee as e").uniqueResult());
    }　　

    多态查询：

　　HQL不仅会查询出该持久化类的全部实例，还会查询出该类的子类的全部实例，前提是存在继承映射。

　　HQL查询的where子句：

　　where子句主要用于筛选选中的结果，缩小选择的范围，如：

复制代码 代码如下:

from employee as e where e.name like "xjg%"    @Test
    public void testHQLWhere() {
        Session session = HibernateUtil.getOpenSession();
        List<Employee> employeeList = session.createQuery("from Employee as e where e.name like 'zhou%'").list();
        for(Employee e : employeeList)
            System.out.println(e);
    }　　

    order by子句：

　　查询返回结合可以根据类或组件属性的任何属性进行排序，还可以使用asc或desc关键字指定升序或者降序，如：

from Employee as e order by e.name desc　　

子查询：

　　子查询中就是查询语句中还有查询语句，如：

复制代码 代码如下:

from Employee as e where e.age > (select p.age from Person as p)    @Test
    public void testHQLChildQuery() {
        Session session = HibernateUtil.getOpenSession();
        List<Employee> employeeList = session.createQuery("from Employee as e where e.age > (select e1.age from Employee as e1 where e1.name = 'xujianguo')").list();
        for(Employee e : employeeList)
            System.out.println(e);
    }　　
[code]

    命名查询：

HQL查询还支持将查询所用的HQL语句放入配置文件中，而不是代码中，在Hibernate映射文件的<hibernate-mapping>元素中使用<query>子元素来定义命名查询，这个<query>元素只需指定一个name属性，指定该命名查询的名字 ，如：

[code]
<query name="query">
    from Employee as e
<query />　　

Session里提供了一个getNamedQuery(String name)方法，该方法用于创建一个Query对象，一旦获得Query对象，剩下的工作就跟前面的一样了。

复制代码 代码如下:

    @Test
    public void testHQLNamedQuery() {
        Session session = HibernateUtil.getOpenSession();
        List<Employee> employeeList = session.getNamedQuery("query").list();
        for(Employee e : employeeList)
            System.out.println(e);
    }

HQL 查询语句

/**
 *
 */
package com.b510.example;

import java.util.Iterator;
import java.util.List;
import java.util.Map;

import org.hibernate.Criteria;
import org.hibernate.FetchMode;
import org.hibernate.Query;
import org.hibernate.Session;

/**
 *
 * @author XHW
 *
 * @date 2011-6-18
 *
 */
public class HibernateTest {

 /**
  * @param args
  */
 public static void main(String[] args) {
  HibernateTest test = new HibernateTest();
  test.where();
  test.function();
  test.update();
  test.jiaoChaCheck();
  test.innerJoin();
  test.QBC();
  test.leftOuterJoin();
  test.rightOuterJoin();
 }

 public void where() {
  // 使用where查询
  Session session = HibernateSessionFactoryUtil.getSessionFactory()
    .openSession();
  session.beginTransaction();
  Query query = session
    .createQuery("from User where id not between 200 and 2000");
  List<User> list = query.list();

  for (User user : list) {
   System.out.println(user.getId() + user.getUsername());
  }
  // 投影查询 中使用where子句
  query = session.createQuery("select username from User where id=2");
  List<String> listname = query.list();

  for (String name : listname) {
   System.out.println(name);
  }
  // in查询
  query = session
    .createQuery("from User where username in ('Hongten','Hanyuan','dfgd')");
  List<User> listin = query.list();

  for (User user : listin) {
   System.out.println(user.getId() + user.getUsername());
  }
  // like查询
  query = session.createQuery("from User where username not like 'Hon%'");
  List<User> listlike = query.list();

  for (User user : listlike) {
   System.out.println(user.getId() + user.getUsername());
  }
  // null查询
  query = session.createQuery("from User where password is null");
  List<User> listnull = query.list();

  for (User user : listnull) {
   System.out.println(user.getId() + user.getUsername());
  }
  // and查询
  query = session
    .createQuery("from User where password is not null and id<5");
  List<User> listand = query.list();

  for (User user : listand) {
   System.out.println(user.getId() + user.getUsername()
     + user.getPassword());
  }
  // order by
  query = session.createQuery("from User order by username,id desc");
  List<User> listorderby = query.list();

  for (User user : listorderby) {
   System.out.println(user.getId() + user.getUsername());
  }
  // 使用"?"号 作为参数占位符，一条HQL语句中可以使用多个？
  // query.setInteger(0,2)
  // query.setString(0,"Hongten")
  query = session
    .createQuery("select username from User where username=?");
  query.setString(0, "Hongten");
  List<String> listwenhao = query.list();
  for (String name : listwenhao) {
   System.out.println(name);
  }

  session.getTransaction().commit();

 }

 public void function() {// 把大写字母转化为小写字母
  // 作用可以用在：比如在一个用户注册的程序中，大小写不容易区分，但是全部转化为小写后就可以很容易进行比较
  Session session = HibernateSessionFactoryUtil.getSessionFactory()
    .openSession();
  session.beginTransaction();
  // 输出原始的数据
  Query query = session.createQuery("select username from User");
  List<String> list = query.list();

  for (String name : list) {
   System.out.println(name);
  }
  System.out.println("-------------------------------------------");
  // 输出的数据全部转化为小写
  query = session.createQuery("select lower(username) from User");
  List<String> listChange = query.list();

  for (String name : listChange) {
   System.out.println(name);
  }
  session.getTransaction().commit();
 }

 public void update() {
  Session session = HibernateSessionFactoryUtil.getSessionFactory()
    .openSession();
  session.beginTransaction();
  Query query = session
    .createQuery("update User set username='洪伟1231' where id=?");
  query.setInteger(0, 3);
  int rowCount = query.executeUpdate();
  System.out.println(rowCount);
  session.getTransaction().commit();
 }

 public void operateProfile() {// 对profile这个类执行HQL语句操作
  Session session = HibernateSessionFactoryUtil.getSessionFactory()
    .openSession();
  session.beginTransaction();
  // 执行查询操作
  Query query = session.createQuery("from Profile");
  List<Profile> list = query.list();
  for (Profile profile : list) {
   System.out.println(profile.getId() + profile.getEmail()
     + profile.getAddress() + profile.getMobile()
     + profile.getPostcode());
  }
  // 执行删除操作
  query = session.createQuery("delete from Profile where id=?");
  query.setInteger(0, 3);
  int rowCount = query.executeUpdate();
  System.out.println(rowCount);
  session.getTransaction().commit();
 }

 public void jiaoChaCheck() {//交叉查询
  //这种方法查询出来的结果是笛卡尔积，对于我们开发中没有多大用处
  Session session = HibernateSessionFactoryUtil.getSessionFactory()
    .openSession();
  session.beginTransaction();
  Query query=session.createQuery("from User,Profile");

  List<Object[]> list=query.list();

  for(Object[] values:list){
   User user=(User)values[0];
   System.out.print("ID :"+user.getId()+",UserName:"+user.getUsername()+",Password:"+user.getPassword());
   Profile profile=(Profile)values[1];
   System.out.println(profile.getEmail()+profile.getMobile()+profile.getAddress()+profile.getPostcode());
  }

  session.getTransaction().commit();
 }

 public void innerJoin(){//内连接查询
  /**
   * 下面三种hql语句都是可以得到相同的结果
   * String hql="select p from Profile as p inner join p.user";
   * 在下面的hql语句中加入"fetch"后，此hql语句变为了"迫切HQL"语句，这样的查询效率要比上面的hql语句要高
   * String hql="select p from Profile as p inner join fetch p.user";
   *
   * String hql="select p from Profile p,User u where p.user=u";
   * String hql="select p from Profile p,User u where p.user.id=u.id";
   * 
   */ 
  Session session = HibernateSessionFactoryUtil.getSessionFactory()
    .openSession();
  session.beginTransaction();
  String hql="select p from Profile as p inner join fetch p.user";
  //String hql="select p from Profile p,User u where p.user=u";
  //String hql="select p from Profile p,User u where p.user.id=u.id";
  Query query=session.createQuery(hql);
  List<Profile> list=query.list();
  for(Profile p:list){
   System.out.println("ID:"+p.getUser().getId()+"   Username: "+p.getUser().getUsername()+"   Email: "+p.getEmail()+",   Address: "+p.getAddress());
  }
  session.getTransaction().commit();
  }

 public void QBC(){//QBC中实现内连接查询
  Session session=HibernateSessionFactoryUtil.getSessionFactory().openSession();
  session.beginTransaction();
  Criteria criteria=session.createCriteria(Profile.class).createCriteria("user");
  List<Profile> list=criteria.list();

  for(Profile p:list){
   System.out.println("ID:"+p.getUser().getId()+"   Username: "+p.getUser().getUsername()+"   Email: "+p.getEmail()+",   Address: "+p.getAddress());
  }
  //QBC中实现外连接
  System.out.println("##################################################");
  criteria=session.createCriteria(Profile.class).setFetchMode("user", FetchMode.JOIN);
  List<Profile> listp=criteria.list();

  for(Profile p:list){
   System.out.println("ID:"+p.getUser().getId()+"   Username: "+p.getUser().getUsername()+"   Email: "+p.getEmail()+",   Address: "+p.getAddress());   
  } 
  session.getTransaction().commit();
 }

 public void leftOuterJoin(){//左外连接
  /**
   * String hql="select p from Profile p left outer join p.user order by p.user.id";
   * 在下面的hql语句中加入"fetch"后，此hql语句变为了"迫切HQL"语句，这样的查询效率要比上面的hql语句要高
   * String hql="select p from Profile p left outer join fetch p.user order by p.user.id";
   *
   * String hqlu="select u from User u left outer join u.profiles";
   *  在下面的hql语句中加入"fetch"后，此hql语句变为了"迫切HQL"语句，这样的查询效率要比上面的hql语句要高
   * String hqlu="select u from User u left outer join fetch u.profiles";
   */
  Session session=HibernateSessionFactoryUtil.getSessionFactory().getCurrentSession();
  session.beginTransaction();
  String hql="select p from Profile p left outer join fetch p.user order by p.user.id";
  Query query=session.createQuery(hql);

  List<Profile> list=query.list();
  for(Profile p:list){
   System.out.println("ID:"+p.getUser().getId()+"   Username: "+p.getUser().getUsername()+"   Email: "+p.getEmail()+",   Address: "+p.getAddress());
  }

  System.out.println("-------------------------------------");
  String hqlu="select u from User u left outer join fetch u.profiles";
  query=session.createQuery(hqlu);

  List<User> listu=query.list();
  for(User u:listu){
   System.out.println(u.getId()+u.getUsername()+u.getProfiles());
  }
  session.getTransaction().commit();

 }

 public void rightOuterJoin(){//右外连接
  Session session=HibernateSessionFactoryUtil.getSessionFactory().getCurrentSession();
  session.beginTransaction();
  String hql="select u from User u right outer join u.profiles order by u.id";
  Query query=session.createQuery(hql);

  List<User> listu=query.list();
  for(User user:listu){
   System.out.println(user.getId()+user.getUsername()+user.getProfiles());
  }

  session.getTransaction().commit();

 }

}

结果：

log4j:WARN No appenders could be found for logger (org.hibernate.cfg.Environment).
log4j:WARN Please initialize the log4j system properly.
Hibernate:
    select
        user0_.id as id0_,
        user0_.username as username0_,
        user0_.password as password0_
    from
        users.user user0_
    where
        user0_.id not between 200 and 2000
1hongten
2hanyuan
3hongwei
4mingliu
5shouzhang
Hibernate:
    select
        user0_.username as col_0_0_
    from
        users.user user0_
    where
        user0_.id=2
hanyuan
Hibernate:
    select
        user0_.id as id0_,
        user0_.username as username0_,
        user0_.password as password0_
    from
        users.user user0_
    where
        user0_.username in (
            'Hongten' , 'Hanyuan' , 'dfgd'
        )
1hongten
2hanyuan
Hibernate:
    select
        user0_.id as id0_,
        user0_.username as username0_,
        user0_.password as password0_
    from
        users.user user0_
    where
        user0_.username not like 'Hon%'
2hanyuan
4mingliu
5shouzhang
Hibernate:
    select
        user0_.id as id0_,
        user0_.username as username0_,
        user0_.password as password0_
    from
        users.user user0_
    where
        user0_.password is null
Hibernate:
    select
        user0_.id as id0_,
        user0_.username as username0_,
        user0_.password as password0_
    from
        users.user user0_
    where
        (
            user0_.password is not null
        )
        and user0_.id<5
1hongten123
2hanyuan5645645
3hongwei5645645
4mingliu5645645
Hibernate:
    select
        user0_.id as id0_,
        user0_.username as username0_,
        user0_.password as password0_
    from
        users.user user0_
    order by
        user0_.username,
        user0_.id desc
2hanyuan
1hongten
3hongwei
4mingliu
5shouzhang
Hibernate:
    select
        user0_.username as col_0_0_
    from
        users.user user0_
    where
        user0_.username=?
hongten
Hibernate:
    select
        user0_.username as col_0_0_
    from
        users.user user0_
hongten
hanyuan
hongwei
mingliu
shouzhang
-------------------------------------------
Hibernate:
    select
        lower(user0_.username) as col_0_0_
    from
        users.user user0_
hongten
hanyuan
hongwei
mingliu
shouzhang
Hibernate:
    update
        users.user
    set
        username='Hongwei1231'
    where
        id=?
1
Hibernate:
    select
        user0_.id as id0_0_,
        profile1_.id as id1_1_,
        user0_.username as username0_0_,
        user0_.password as password0_0_,
        profile1_.user_id as user2_1_1_,
        profile1_.email as email1_1_,
        profile1_.phone as phone1_1_,
        profile1_.mobile as mobile1_1_,
        profile1_.address as address1_1_,
        profile1_.postcode as postcode1_1_
    from
        users.user user0_,
        users.profile profile1_
ID :1,UserName:hongten,Password:123hongtenzone@foxmail.com45464Guangzhoushi65465
ID :1,UserName:hongten,Password:123hanyuan@foxmail.com45648255GuangzhoushiDianbian65465
ID :1,UserName:hongten,Password:123hanyuan@foxmail.com45648255GuangzhoushiDianbian65465
ID :2,UserName:hanyuan,Password:5645645hongtenzone@foxmail.com45464Guangzhoushi65465
ID :2,UserName:hanyuan,Password:5645645hanyuan@foxmail.com45648255GuangzhoushiDianbian65465
ID :2,UserName:hanyuan,Password:5645645hanyuan@foxmail.com45648255GuangzhoushiDianbian65465
ID :3,UserName:Hongwei1231,Password:5645645hongtenzone@foxmail.com45464Guangzhoushi65465
ID :3,UserName:Hongwei1231,Password:5645645hanyuan@foxmail.com45648255GuangzhoushiDianbian65465
ID :3,UserName:Hongwei1231,Password:5645645hanyuan@foxmail.com45648255GuangzhoushiDianbian65465
ID :4,UserName:mingliu,Password:5645645hongtenzone@foxmail.com45464Guangzhoushi65465
ID :4,UserName:mingliu,Password:5645645hanyuan@foxmail.com45648255GuangzhoushiDianbian65465
ID :4,UserName:mingliu,Password:5645645hanyuan@foxmail.com45648255GuangzhoushiDianbian65465
ID :5,UserName:shouzhang,Password:5645645hongtenzone@foxmail.com45464Guangzhoushi65465
ID :5,UserName:shouzhang,Password:5645645hanyuan@foxmail.com45648255GuangzhoushiDianbian65465
ID :5,UserName:shouzhang,Password:5645645hanyuan@foxmail.com45648255GuangzhoushiDianbian65465
Hibernate:
    select
        profile0_.id as id1_0_,
        user1_.id as id0_1_,
        profile0_.user_id as user2_1_0_,
        profile0_.email as email1_0_,
        profile0_.phone as phone1_0_,
        profile0_.mobile as mobile1_0_,
        profile0_.address as address1_0_,
        profile0_.postcode as postcode1_0_,
        user1_.username as username0_1_,
        user1_.password as password0_1_
    from
        users.profile profile0_
    inner join
        users.user user1_
            on profile0_.user_id=user1_.id
ID:1   Username: hongten   Email: hongtenzone@foxmail.com,   Address: Guangzhoushi
ID:2   Username: hanyuan   Email: hanyuan@foxmail.com,   Address: GuangzhoushiDianbian
ID:3   Username:Hongwei1231   Email: hanyuan@foxmail.com,   Address: GuangzhoushiDianbian
Hibernate:
    select
        this_.id as id1_1_,
        this_.user_id as user2_1_1_,
        this_.email as email1_1_,
        this_.phone as phone1_1_,
        this_.mobile as mobile1_1_,
        this_.address as address1_1_,
        this_.postcode as postcode1_1_,
        user1_.id as id0_0_,
        user1_.username as username0_0_,
        user1_.password as password0_0_
    from
        users.profile this_
    inner join
        users.user user1_
            on this_.user_id=user1_.id
ID:1   Username: hongten   Email: hongtenzone@foxmail.com,   Address: Guangzhoushi
ID:2   Username: hanyuan   Email: hanyuan@foxmail.com,   Address: GuangzhoushiDianbian
ID:3   Username: Hongwei1231   Email: hanyuan@foxmail.com,   Address: GuangzhoushiDianbian
##################################################
Hibernate:
    select
        this_.id as id1_1_,
        this_.user_id as user2_1_1_,
        this_.email as email1_1_,
        this_.phone as phone1_1_,
        this_.mobile as mobile1_1_,
        this_.address as address1_1_,
        this_.postcode as postcode1_1_,
        user2_.id as id0_0_,
        user2_.username as username0_0_,
        user2_.password as password0_0_
    from
        users.profile this_
    left outer join
        users.user user2_
            on this_.user_id=user2_.id
ID:1   Username: hongten   Email: hongtenzone@foxmail.com,   Address: Guangzhoushi
ID:2   Username: hanyuan   Email: hanyuan@foxmail.com,   Address: GuangzhoushiDianbian
ID:3   Username: 洪伟1231   Email: hanyuan@foxmail.com,   Address: GuangzhoushiDianbian
Hibernate:
    select
        profile0_.id as id1_0_,
        user1_.id as id0_1_,
        profile0_.user_id as user2_1_0_,
        profile0_.email as email1_0_,
        profile0_.phone as phone1_0_,
        profile0_.mobile as mobile1_0_,
        profile0_.address as address1_0_,
        profile0_.postcode as postcode1_0_,
        user1_.username as username0_1_,
        user1_.password as password0_1_
    from
        users.profile profile0_
    left outer join
        users.user user1_
            on profile0_.user_id=user1_.id
    order by
        profile0_.user_id
ID:1   Username: hongten   Email: hongtenzone@foxmail.com,   Address: Guangzhoushi
ID:2   Username: hanyuan   Email: hanyuan@foxmail.com,   Address: GuangzhoushiDianbian
ID:3   Username: 洪伟1231   Email: hanyuan@foxmail.com,   Address: GuangzhoushiDianbian
-------------------------------------
Hibernate:
    select
        user0_.id as id0_0_,
        profiles1_.id as id1_1_,
        user0_.username as username0_0_,
        user0_.password as password0_0_,
        profiles1_.user_id as user2_1_1_,
        profiles1_.email as email1_1_,
        profiles1_.phone as phone1_1_,
        profiles1_.mobile as mobile1_1_,
        profiles1_.address as address1_1_,
        profiles1_.postcode as postcode1_1_,
        profiles1_.user_id as user2_0__,
        profiles1_.id as id0__
    from
        users.user user0_
    left outer join
        users.profile profiles1_
            on user0_.id=profiles1_.user_id
1hongten[com.b510.example.Profile@14eaec9]
2hanyuan[com.b510.example.Profile@569c60]
3Hongwei1231[com.b510.example.Profile@d67067]
4mingliu[]
5shouzhang[]
Hibernate:
    select
        user0_.id as id0_,
        user0_.username as username0_,
        user0_.password as password0_
    from
        users.user user0_
    right outer join
        users.profile profiles1_
            on user0_.id=profiles1_.user_id
    order by
        user0_.id
Hibernate:
    select
        profiles0_.user_id as user2_1_,
        profiles0_.id as id1_,
        profiles0_.id as id1_0_,
        profiles0_.user_id as user2_1_0_,
        profiles0_.email as email1_0_,
        profiles0_.phone as phone1_0_,
        profiles0_.mobile as mobile1_0_,
        profiles0_.address as address1_0_,
        profiles0_.postcode as postcode1_0_
    from
        users.profile profiles0_
    where
        profiles0_.user_id=?
1hongten[com.b510.example.Profile@10c0f66]
Hibernate:
    select
        profiles0_.user_id as user2_1_,
        profiles0_.id as id1_,
        profiles0_.id as id1_0_,
        profiles0_.user_id as user2_1_0_,
        profiles0_.email as email1_0_,
        profiles0_.phone as phone1_0_,
        profiles0_.mobile as mobile1_0_,
        profiles0_.address as address1_0_,
        profiles0_.postcode as postcode1_0_
    from
        users.profile profiles0_
    where
        profiles0_.user_id=?
2hanyuan[com.b510.example.Profile@e265d0]
Hibernate:
    select
        profiles0_.user_id as user2_1_,
        profiles0_.id as id1_,
        profiles0_.id as id1_0_,
        profiles0_.user_id as user2_1_0_,
        profiles0_.email as email1_0_,
        profiles0_.phone as phone1_0_,
        profiles0_.mobile as mobile1_0_,
        profiles0_.address as address1_0_,
        profiles0_.postcode as postcode1_0_
    from
        users.profile profiles0_
    where
        profiles0_.user_id=?
3Hongwei1231[com.b510.example.Profile@8997d1]

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