hibernate HQL

Session session = null;
try {
	session = HibernateSessionFactory.getSessionFactory().getCurrentSession();
	session.beginTransaction();
			
	//FROM子句
	//简单的查询，Employee为实体名而不是数据库中的表名(面向对象特性)  
	//hql = "FROM Employee";  
	//hql = "FROM Employee AS e"; // 使用别名  
	//hql = "FROM Employee e"; // 使用别名，as关键字可省略  
	String hql = "FROM User";
	Query query = session.createQuery(hql);
	List results = query.list();
	System.out.println(results.size());
			
	//WHERE子句
	// 带上过滤条件的（可以使用别名）
	//hql = "FROM Employee WHERE id < 10";  
	//hql = "FROM Employee e WHERE e.id < 10";  
	//hql = "FROM Employee e WHERE e.id < 10 AND e.id > 5";  
	hql = "FROM Role r WHERE r.id = 1";
	query = session.createQuery(hql);
	results = query.list();
	if(results != null & results.size() > 0)
		System.out.println(((Role) results.get(0)).getRoleName());
			
	//ORDER BY 子句
	//带上排序条件的：
	//hql = "FROM Employee e WHERE e.id < 10 ORDER BY e.name";  
	//hql = "FROM Employee e WHERE e.id < 10 ORDER BY e.name DESC";  
	//hql = "FROM Employee e WHERE e.id < 10 ORDER BY e.name DESC, e.id ASC";  
	hql = "FROM Role r WHERE r.id > 0 "
		+ "ORDER BY r.id DESC, r.roleName ASC ";
	query = session.createQuery(hql);
	results = query.list();
	System.out.println(results.size());
			
	//指定select子句（不可以使用select *）  
	//hql = "SELECT e FROM Employee e"; // 相当于"FROM Employee e"  
	//hql = "SELECT e.name FROM Employee e"; // 只查询一个列，返回的集合的元素类型就是这个属性的类型  
	//hql = "SELECT e.id, e.name FROM Employee e"; // 查询多个列，返回的集合的元素类型是Object数组  
	//hql = "SELECT new Employee(e.id, e.name) FROM Employee e"; // 可以使用new语法，指定把查询出的部分属性封装到对象中  
	hql = "SELECT u.userName FROM User u";
	query = session.createQuery(hql);
	//分页查询
	query.setFirstResult(0); 
	query.setMaxResults(10);
	results = query.list();
	for (Object obj : results) {
		String str = (String) obj;
		System.out.println(str);
	}
			
	//聚集函数：count(), max(), min(), avg(), sum()  
	//hql = "SELECT COUNT(*) FROM Employee"; // 返回的结果是Long型的  
	//hql = "SELECT min(id) FROM Employee"; // 返回的结果是id属性的类型  

	//GROUP BY  Having 
	/**
	hql = "SELECT e.name, COUNT(e.id) FROM Employee e GROUP BY e.name";  
	hql = "SELECT e.name, COUNT(e.id) FROM Employee e GROUP BY e.name " + 
		"HAVING count(e.id) > 1";  
	hql = "SELECT e.name, COUNT(e.id) FROM Employee e WHERE id < 9 " + 
		"GROUP BY e.name HAVING count(e.id) > 1";  
	hql = "SELECT e.name, COUNT(e.id) FROM Employee e " + 
		"WHERE e.id < 9 " +  
		"GROUP BY e.name " +   
		"HAVING count(e.id) > 1 " + 
		"ORDER BY count(e.id) ASC";
	hql = "SELECT e.name,COUNT(e.id) AS c FROM Employee e " + 
		"WHERE e.id < 9 " + 
		"GROUP BY e.name " + 
		"HAVING count(e.id) > 1 " + 	// 在having子句中不能使用列别名  
		"ORDER BY c ASC"; 		// 在orderby子句中可以使用列别名  
 	*/
	hql = "SELECT COUNT(*), u.userName FROM User u GROUP BY u.userName ";
	query = session.createQuery(hql);
	results = query.list();
	Object[] arr = (Object[]) results.get(0);
	System.out.println(arr[0] + ", " + arr[1]);
			
	//连接查询 
	// HQL是面向对象的查询  
	//>> 内连接（inner关键字可以省略）  
	//hql = "SELECT e.id, e.name, d.name FROM Employee e JOIN e.department d";  
	//hql = "SELECT e.id, e.name, d.name FROM Employee e INNER JOIN e.department d";  
	//>> 左外连接（outer关键字可以省略）  
	//hql = "SELECT e.id, e.name, d.name FROM Employee e LEFT OUTER JOIN e.department d";  
	//>> 右外连接（outer关键字可以省略）  
	//hql = "SELECT e.id, e.name, d.name FROM Employee e RIGHT JOIN e.department d";  
	//可以使用更方便的方法  
	//hql = "SELECT e.id, e.name, e.department.name FROM Employee e";  
		
	//查询时使用参数  
	// >> 方式一：使用'?'占位  
	/**
	hql = "FROM Employee e WHERE id BETWEEN ? AND ?";  
	List list = session.createQuery(hql)
		.setParameter(0, 5)	// 设置参数，第1个参数的索引为0。  
		.setParameter(1, 15)
		.list();  
			
	// >> 方式二：使用变量名  
	hql = "FROM Employee e WHERE id BETWEEN :idMin AND :idMax";  
	List list = session.createQuery(hql)
		.setParameter("idMax", 15)
		.setParameter("idMin", 5)
		.list();  
			
	// 当参数是集合时，一定要使用setParameterList()设置参数值  
	hql = "FROM Employee e WHERE id IN (:ids)";  
	List list = session.createQuery(hql)
		.setParameterList("ids", new Object[] { 1, 2, 3, 5, 8, 100 })
		.list();
	*/
			
	//update与delete，不会通知Session缓存  
	/**
	// >> Update
	int result = session.createQuery(
		"UPDATE Employee e SET e.name = ? WHERE id > 15")
		.setParameter(0, "无名氏")
		.executeUpdate(); 	// 返回int型的结果，表示影响了多少行。  
	// >> Delete  
	int result1 = session.createQuery(
		"DELETE FROM Employee e WHERE id > 15")
		.executeUpdate();	// 返回int型的结果，表示影响了多少行。  
	*/
			
	session.getTransaction().commit();
			
} catch(Exception e) {
	e.printStackTrace();  
	session.getTransaction().rollback();  
} finally {  
	HibernateSessionFactory.closeSession();  
}

   *  HQL: Hibernate Query Language.
  *  特点： 
  *  >> 1，与SQL相似，SQL中的语法基本上都可以直接使用。 
  *  >> 2，SQL查询的是表和表中的列；HQL查询的是对象与对象中的属性。 
  *  >> 3，HQL的关键字不区分大小写，类名与属性名是区分大小写的。 
  *  >> 4，SELECT可以省略.