|
内连接：把两面共有的部分查出来
左连接：把左边的部分全查出来
右连接：把右边的部分全查出来
/**
* inner join
*/
public void testquery1(){
Session session = null;
try{
session = HibernateUtils2.singleInstance.getSession();
session.beginTransaction();
//可以省略inner，因为只要写了join，默认就是inner内连接
//List lists = (List)session.createQuery("select c.name, s.name from Student s join s.classes c").list();
//写上的话，就是这个样子啦
List lists = (List)session.createQuery("select c.name, s.name from Student s inner join s.classes c").list();
for (Iterator iter = lists.iterator();iter.hasNext();) {
Object[] obj = (Object[])iter.next();
System.out.println(obj[0] + "," + obj[1]);
}
}catch(Exception e){
e.printStackTrace();
session.getTransaction().rollback();
}finally{
HibernateUtils2.singleInstance.closeSession(session);
}
}
/**
* left join
*/
public void testquery2(){
Session session = null;
try{
session = HibernateUtils2.singleInstance.getSession();
session.beginTransaction();
//把没有班级的学生也查出来，注意left join 后接的表有点特殊，是c.student即班级中的student属性，hibernate会依照这个属性帮我们找到相应的表
List lists = (List)session.createQuery("select c.name, s.name from Student s left join c.student s").list();
for (Iterator iter = lists.iterator();iter.hasNext();) {
Object[] obj = (Object[])iter.next();
System.out.println(obj[0] + "," + obj[1]);
}
}catch(Exception e){
e.printStackTrace();
session.getTransaction().rollback();
}finally{
HibernateUtils2.singleInstance.closeSession(session);
}
}
/**
* right join
*/
public void testquery2(){
Session session = null;
try{
session = HibernateUtils2.singleInstance.getSession();
session.beginTransaction();
//把没有学生的班级也查出来，注意right join 后接的也比较特殊，理由同上
List lists = (List)session.createQuery("select c.name, s.name from Student s right join c.student s").list();
for (Iterator iter = lists.iterator();iter.hasNext();) {
Object[] obj = (Object[])iter.next();
System.out.println(obj[0] + "," + obj[1]);
}
}catch(Exception e){
e.printStackTrace();
session.getTransaction().rollback();
}finally{
HibernateUtils2.singleInstance.closeSession(session);
}
} | 
转播
