Hibernate学习36 -- Hibernate查询语言（HQL）10 -- 使用聚集函数查询

聚集函数查询：

l         count(*)

l         avg(...)

l         sum(...)

l         min(...)

l         max(...)

l         count(...)

例子代码如下：

/**  * 统计查询  */ 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);        }     }      }