Hsql 查询_sql数据查询

全栈程序员站长

发布于 2022-11-09 08:57:21

1.5K0

文章被收录于专栏：全栈程序员必看全栈程序员必看

大家好，又见面了，我是你们的朋友全栈君。

还是班级，学生，课程，学生选课，四张表初始值：

1，查询所有的学生

session.createQuery("from Student s").list()

sql语句：

Hibernate: 
    select
        student0_.stu_id as stu1_0_,
        student0_.class_id as class5_0_,
        student0_.stu_birth as stu2_0_,
        student0_.stu_name as stu3_0_,
        student0_.stuSex as stuSex0_ 
    from
        tb_student student0_

2，将学生表和课程表做隐式连接查询：

session.createQuery("from Student s  where s.stuCourses.stuCourseId>:id").setInteger("id", 0).list();

出现异常： org.hibernate.QueryException: illegal attempt to dereference collection原因是在Hibernate 3.0 以后对关联实体是集合的属性，不能直接使用隐式连接查询，改成：

Session session=HibernateSessionFactory.getSession();
		List<Object[]> scs=session.createQuery("from Student s inner join s.stuCourses sc where sc.stuCourseId>:id").setInteger("id", 0).list();
		//List<Object[]> scs=session.createQuery("from Student s  where s.stuCourses.stuCourseId>:id").setInteger("id", 0).list();
		for(Object[] o:scs){
			Student s=(Student)o[0];
			StuCourse sc= (StuCourse)o[1];
			System.out.println("stuName:"+s.getStuName()+"stuCourseName："+sc.getCourse().getCourseName());
		}

结果：

Hibernate: 
    select
        student0_.stu_id as stu1_0_0_,
        stucourses1_.sc_id as sc1_2_1_,
        student0_.class_id as class5_0_0_,
        student0_.stu_birth as stu2_0_0_,
        student0_.stu_name as stu3_0_0_,
        student0_.stuSex as stuSex0_0_,
        stucourses1_.course_id as course4_2_1_,
        stucourses1_.sc_score as sc2_2_1_,
        stucourses1_.sc_time as sc3_2_1_,
        stucourses1_.stu_id as stu5_2_1_ 
    from
        tb_student student0_ 
    inner join
        tb_stuCourse stucourses1_ 
            on student0_.stu_id=stucourses1_.stu_id 
    where
        stucourses1_.sc_id>?

生成的集合的元素，是由Student，和StuCourse两个实体组成的数组，如果只需要保留一个实体 hsql改成：

session.createQuery("select s from Student s inner join s.stuCourses sc where sc.stuCourseId>:id").setInteger("id", 0).list();

3，使用 left/right out join 查询：

session.createQuery(“select s from Student s left outer join s.stuCourses sc”).list();

生成的sql语句：

Hibernate: 
    select
        student0_.stu_id as stu1_0_,
        student0_.class_id as class5_0_,
        student0_.stu_birth as stu2_0_,
        student0_.stu_name as stu3_0_,
        student0_.stuSex as stuSex0_ 
    from
        tb_student student0_ 
    left outer join
        tb_stuCourse stucourses1_ 
            on student0_.stu_id=stucourses1_.stu_id

right outer join：

session.createQuery("select s from Student s right outer join s.stuCourses sc").list();

sql：

Hibernate: 
    select
        student0_.stu_id as stu1_0_,
        student0_.class_id as class5_0_,
        student0_.stu_birth as stu2_0_,
        student0_.stu_name as stu3_0_,
        student0_.stuSex as stuSex0_ 
    from
        tb_student student0_ 
    right outer join
        tb_stuCourse stucourses1_ 
            on student0_.stu_id=stucourses1_.stu_id

4，使用分页查询：

(List<Student>)session.createQuery(“from Student s”).setFirstResult(1).setMaxResults(2).list();

setFirstResult（）从哪条记录开始，setMaxResult()每次取多少条记录

Hibernate: 
    select
        student0_.stu_id as stu1_0_,
        student0_.class_id as class5_0_,
        student0_.stu_birth as stu2_0_,
        student0_.stu_name as stu3_0_,
        student0_.stuSex as stuSex0_ 
    from
        tb_student student0_ limit ?,
        ?

在MySql里面调用的还是 limit 关键字来进行分页

5，使用条件查询：

//学生根据班级，性别，出生年月进行查询
	public List<Student> getRightStudent(){// 使用条件查询
		Session session=HibernateSessionFactory.getSession();
		return session.createCriteria(Student.class).add(Restrictions.eq("stuSex", true)).createCriteria("myClass").add(Restrictions.eq("classId", 1)).list();
	}

注意，虽然添加了导航属性“myClass” 但最终结果的元素还是 Student 实体看sql：

Hibernate: 
    select
        this_.stu_id as stu1_0_1_,
        this_.class_id as class5_0_1_,
        this_.stu_birth as stu2_0_1_,
        this_.stu_name as stu3_0_1_,
        this_.stuSex as stuSex0_1_,
        theclass1_.classId as classId1_0_,
        theclass1_.className as className1_0_ 
    from
        tb_student this_ 
    inner join
        tb_class theclass1_ 
            on this_.class_id=theclass1_.classId 
    where
        this_.stuSex=? 
        and theclass1_.classId=?

发布者：全栈程序员栈长，转载请注明出处：https://javaforall.cn/190666.html原文链接：https://javaforall.cn

本文参与腾讯云自媒体同步曝光计划，分享自作者个人站点/博客。

原始发表：2022年9月22日，如有侵权请联系 cloudcommunity@tencent.com 删除

sql