Hibernate的批量查询——HQL
2024-10-21 06:46:36
HQL(Hibernate Query Language)查询:
1、查询所有学生信息:
public static void testSel() {
Session session = HibernateUtils.openSession();
Transaction transaction = session.beginTransaction();
String hql="from pers.zhb.domain.Student";
Query query= session.createQuery(hql);
List<Student>list=query.list();
System.out.println(list);
transaction.commit();
session.close();//游离状态
}
简化写法:
public static void testSel() {
Session session = HibernateUtils.openSession();
Transaction transaction = session.beginTransaction();
String hql="from Student";
Query query= session.createQuery(hql);
List<Student> list=query.list();
System.out.println(list);
transaction.commit();
session.close();//游离状态
}
查询所有表的数据:
public static void testSel() {
Session session = HibernateUtils.openSession();
Transaction transaction = session.beginTransaction();
String hql="from java.lang.Object";
Query query= session.createQuery(hql);
List<Object> list=query.list();
System.out.println(list);
transaction.commit();
session.close();//游离状态
}
2、条件查询(查询所有的女学生的信息):
public static void testSel() {
Session session = HibernateUtils.openSession();
Transaction transaction = session.beginTransaction();
String hql="from pers.zhb.domain.Student where sex='女'";
Query query= session.createQuery(hql);
List<Student>list=query.list();
System.out.println(list);
transaction.commit();
session.close();//游离状态
}
3、问号占位符的使用:
public static void testSel() {
Session session = HibernateUtils.openSession();
Transaction transaction = session.beginTransaction();
String hql="from pers.zhb.domain.Student where studentno=?";
Query query= session.createQuery(hql);
query.setInteger(,);
Student student= (Student) query.uniqueResult();//获取唯一值
System.out.println(student);
transaction.commit();
session.close();
}
public static void testSel() {
Session session = HibernateUtils.openSession();
Transaction transaction = session.beginTransaction();
String hql="from pers.zhb.domain.Student where sex=?";
Query query= session.createQuery(hql);
//query.setFetchSize(0,"女");
query.setParameter(,"女");//通用
List<Student> list=query.getResultList();
System.out.println(list);
transaction.commit();
session.close();
}
4、命名占位符:
省去了用数字指明属性位置的麻烦,直接用属性名代替。
public static void testSel() {
Session session = HibernateUtils.openSession();
Transaction transaction = session.beginTransaction();
String hql="from pers.zhb.domain.Student where sex=:sex";
Query query= session.createQuery(hql);
query.setParameter("sex","女");//通用
List<Student> list=query.getResultList();
System.out.println(list);
transaction.commit();
session.close();
}
5、分页查询:
需要指明从哪开始,要取几条数据:
public static void testSel() {
Session session = HibernateUtils.openSession();
Transaction transaction = session.beginTransaction();
String hql="from pers.zhb.domain.Student where sex=:sex";
Query query= session.createQuery(hql);
query.setFirstResult();//从0开始
query.setMaxResults();//抓取两条数据
query.setParameter("sex","女");//通用
List<Student> list=query.getResultList();
System.out.println(list);
transaction.commit();
session.close();
}
6、排序查询:
(1)按学号升序排列:
public static void testSel() {
Session session = HibernateUtils.openSession();
Transaction transaction = session.beginTransaction();
String hql="from pers.zhb.domain.Student order by studentno asc";
Query query= session.createQuery(hql);
List<Student> list=query.list();
System.out.println(list);
transaction.commit();
session.close();//游离状态
}
(2)分数降序:
public static void testSel() {
Session session = HibernateUtils.openSession();
Transaction transaction = session.beginTransaction();
String hql="from pers.zhb.domain.Student order by point desc ";
Query query= session.createQuery(hql);
List<Student> list=query.list();
System.out.println(list);
transaction.commit();
session.close();//游离状态
}
7、统计查询:
(1)count:
public static void testSel() {
Session session = HibernateUtils.openSession();
Transaction transaction = session.beginTransaction();
String hql="select count(*) from pers.zhb.domain.Student";
Query query= session.createQuery(hql);
Number number= (Number) query.uniqueResult();
System.out.println(number);
transaction.commit();
session.close();//游离状态
}
(2)sum求所有学生的分数和:
public static void testSel() {
Session session = HibernateUtils.openSession();
Transaction transaction = session.beginTransaction();
String hql="select sum(point) from pers.zhb.domain.Student";
Query query= session.createQuery(hql);
Number number= (Number) query.uniqueResult();
System.out.println(number);
transaction.commit();
session.close();//游离状态
}
(3)avg求平均分:
public static void testSel() {
Session session = HibernateUtils.openSession();
Transaction transaction = session.beginTransaction();
String hql="select avg(point) from pers.zhb.domain.Student";
Query query= session.createQuery(hql);
Number number= (Number) query.uniqueResult();
System.out.println(number);
transaction.commit();
session.close();//游离状态
}
(4)min求最低分:
public static void testSel() {
Session session = HibernateUtils.openSession();
Transaction transaction = session.beginTransaction();
String hql="select min(point) from pers.zhb.domain.Student";
Query query= session.createQuery(hql);
Number number= (Number) query.uniqueResult();
System.out.println(number);
transaction.commit();
session.close();//游离状态
}
8、投影:
(1)查询每个学生的名字:
public static void testSel() {
Session session = HibernateUtils.openSession();
Transaction transaction = session.beginTransaction();
String hql="select sname from pers.zhb.domain.Student";
Query query= session.createQuery(hql);
List list= query.list();
System.out.println(list);
transaction.commit();
session.close();//游离状态
}
(2)查询学生的姓名和学号:
创建构造方法(用于存储姓名和学号):
public Student(Integer studentno,String sname){
super();
this.studentno=studentno;
this.sname=sname;
}
public static void testSel() {
Session session = HibernateUtils.openSession();
Transaction transaction = session.beginTransaction();
String hql="select new Student(studentno,sname) from pers.zhb.domain.Student";
Query query= session.createQuery(hql);
List<Object[]> list= query.list();
System.out.println(list);
transaction.commit();
session.close();//游离状态
}
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