HQL链接查询

和SQL查询一样，HQL也支持各种各样的连接查询，如内连接、外连接。我们知道在SQL中可通过join字句实现多表之间的连接查询。HQL同样提供了连接查询机制，还允许显示指定迫切内连接和迫切左外连接。HQL提供的连接方式如下表所示。

//迫切内连接查询
    @Test
    public void test1() {
        Query query = session.createQuery("select distinct s from Pro s inner join fetch s.emps");
        List<Pro> list = query.list();
        for (Pro item : list
                ) {
            System.out.println(item.getProname());
            for (Emp itme1 : item.getEmps()
                    ) {
                System.out.println(itme1.getEmpname());
            }
        }
    }
//左外链接
    @Test
    public void test2() {
        Query query = session.createQuery("select distinct s from Pro s left outer join  s.emps");
        List<Pro> list = query.list();
        for (Pro item : list
                ) {
            System.out.println(item.getProname());
            for (Emp itme1 : item.getEmps()
                    ) {
                System.out.println(itme1.getEmpname());
            }
        }
    }
//迫切左外链接
    @Test
    public void test3() {
        Query query = session.createQuery("select distinct s from Pro s left outer join fetch s.emps");
        List<Pro> list = query.list();
        for (Pro item : list
                ) {
            System.out.println(item.getProname());
            for (Emp itme1 : item.getEmps()
                    ) {
                System.out.println(itme1.getEmpname());
            }
        }
    }
//右链接
    @Test
    public void test4() {
        Query query = session.createQuery("select distinct s from Pro s right  join s.emps");
        List<Pro> list = query.list();
        for (Pro item : list
                ) {
            System.out.println(item.getProname());
            for (Emp itme1 : item.getEmps()
                    ) {
                System.out.println(itme1.getEmpname());
            }
        }
    }