Hibernate（分组查询等续）

投影查询
使用聚集函数
在HQL中可以调用
Count：统计函数
Min：求最小值函数
Max：求最大值函数
Sum：求和函数
Avg：求平均数函数

Count：统计函数
Session session = HibernateSessionFactory.getSession();
Transaction tx = session.beginTransaction();
Integer count = (Integer)session.createQuery("select count(*) from Hx").uniqueResult();
System.out.print(count);
tx.commit();
session.close();
Avg：求平均数函数
Session session = HibernateSessionFactory.getSession();
Transaction tx = session.beginTransaction();
Float count = (Float)session.createQuery("select avg(c.id) from Hx c").uniqueResult();
System.out.print(count);
tx.commit();
session.close();
Sum：求和函数
Session session = HibernateSessionFactory.getSession();
Transaction tx = session.beginTransaction();
Integer count = (Integer)session.createQuery("select sum(c.id) from Hx c").uniqueResult();
System.out.print(count);
tx.commit();
session.close();
Min：求最小值函数 Max：求最大值函数
Session session = HibernateSessionFactory.getSession();
Transaction tx = session.beginTransaction();
Object[] count = (Object[])session.createQuery("select min(c.age),max(c.age) from Hx c").uniqueResult();
String min = (String)count[0];
String max = (String)count[1];
System.out.print("min="+min+"|max="+max);
tx.commit();
session.close();
分组查询
Session session = HibernateSessionFactory.getSession();
Transaction tx = session.beginTransaction();
Iterator it = session.createQuery("select c.name,count(c) from Hx c group by c.name").iterate();
while(it.hasNext())
{
Object[] oc = (Object[])it.next();
String count = (Integer)oc[1];
System.out.println(name+":"+count);
}
tx.commit();
session.close();