Hibernate HQL 聚合函数 简单实例

常用的聚合函数：

count(*)
avg(...)
sum(...)
min(...)
max(...)
count(...)

简单实例：

public class StatQueryTest extends TestCase {
 
    public void testQuery1() {
       Session session = null;
       try {
           session = HibernateUtils.getSession();
           session.beginTransaction();       
           Long count = (Long)session.createQuery("select count(*) from Student").uniqueResult();
           System.out.println(count);     
           session.getTransaction().commit();
       }catch(Exception e) {
           e.printStackTrace();
           session.getTransaction().rollback();
       }finally {
           HibernateUtils.closeSession(session);
       }
    }  
	
    public void testQuery2() {
       Session session = null;
       try {
           session = HibernateUtils.getSession();
           session.beginTransaction();       
           List students =session.createQuery("select c.name, count(s) from Student s join s.classes c "+"group by c.name order by c.name").list();
           for (Iterator iter=students.iterator(); iter.hasNext();) {
              Object[] obj = (Object[])iter.next();
              System.out.println(obj[0] + ", " + obj[1]);
           }         
           session.getTransaction().commit();
       }catch(Exception e) {
           e.printStackTrace();
           session.getTransaction().rollback();
       }finally {
           HibernateUtils.closeSession(session);
       }
    }     
}