多表的查询进行使用HQL语句进行查询，HQL语句和SQL语句的查询语法比较类似
内连接查询
显示内连接
select * from customer c inner join orders o on c.cid = o.cno 隐式内连接
select * from customers c.orders o where c.cid = o.cno; 外连接查询
左连接查询
select * from customers c left join orders o on c.cid = o.cno 右连接查询
select * from customer c right join orders o on c.cid = o.cno
HQL 的多表查询
迫切和非迫切
非迫切返回结果是Object[]迫切连接返回的结果是对象，把客户的信息封装到客户的对象中，把订单信息封装到客户的set集合中。
内连接查询
内连接使用 inner join，默认返回的是Object数组
Session session = HibernateUtils.getCurrentSession();
Transaction tr = session.beginTransaction();
List<Customer> list = session.beginTransaction();
Set<Customer> set = new HashSet<Customer>(list);
for(Customer customer:set){
System.out.println(customer);
}
tr.commit();
迫切内连接 ：inner join fetch,返回的是实体对象
Session session = HibernateUtils.getCurrentSession();
Transaction tr = session.beginTransaction();
List<Customer> list = session.createQuery("from Customer c inner join fetch c.linkmans").list();
Set<Customer> set = new HashSet<Customer>(list);//去掉重复
for(Customer customer : set){
System.out.println(customer);
}
tr.commit;
左外连接查询
左外连接：封装成List<Object[]>
迫切左外连接
Session session = HIbernateUtils.getCurrentSession();
Transaction tr = session.beginTransaction();
List<Customer> list = session.createQuery("from Customer c left join fetch c.linkmans").list();
for(Customer customer : set){
System.out.println(customer);
}
tr.commit();
