HQL (九) 连接查询

http://wlh269.iteye.com/blog/322050

连接查询（重要）
* 内连接
* 外连接（左连接/右连接）
参见：JoinQueryTest.java

内连接有三种：inner join ，join，“=”

packagecom.wlh.hibernate;

 importjava.util.Iterator;
 importjava.util.List;

 importjunit.framework.TestCase;

 importorg.hibernate.Session;

 publicclassJoinQueryTestextendsTestCase{

 /**
*内联结
*/
 publicvoidtestQuery1(){
 Sessionsession=null;
 try{
session=HibernateUtils.getSession();
session.beginTransaction();
 //====关键字join==========//
 Liststudents=session.createQuery("selects.name,c.namefromStudentsjoins.classesc").list();
 for(Iteratoriter=students.iterator();iter.hasNext();){
Object[]o=(Object[])iter.next();
 System.out.println("id="+o[0]+",o[1]"+o[0]);
}
session.getTransaction().commit();
 }catch(Exceptione){
e.printStackTrace();
session.getTransaction().rollback();
 }finally{
HibernateUtils.closeSession(session);
}
}

 /**
*内联结
*/
 publicvoidtestQuery2(){
 Sessionsession=null;
 try{
session=HibernateUtils.getSession();
session.beginTransaction();
 //=======关键字innerjoin默认就是内连接，所以inner可以加上，也可以省略======//
 Liststudents=session.createQuery("selects.name,c.namefromStudentsinnerjoins.classesc").list();
 for(Iteratoriter=students.iterator();iter.hasNext();){
Object[]o=(Object[])iter.next();
 System.out.println("id="+o[0]+",o[1]"+o[0]);
}
session.getTransaction().commit();
 }catch(Exceptione){
e.printStackTrace();
session.getTransaction().rollback();
 }finally{
HibernateUtils.closeSession(session);
}
}

 /**
*内联结
*/
 publicvoidtestQuery3(){
 Sessionsession=null;
 try{
session=HibernateUtils.getSession();
session.beginTransaction();
 //===========用"="实现内联===========//
 Liststudents=session.createQuery("selects.name,c.namefromStudents,Classescwheres.classes.id=c.id").list();
 for(Iteratoriter=students.iterator();iter.hasNext();){
Object[]o=(Object[])iter.next();
 System.out.println("id="+o[0]+",o[1]"+o[0]);
}
session.getTransaction().commit();
 }catch(Exceptione){
e.printStackTrace();
session.getTransaction().rollback();
 }finally{
HibernateUtils.closeSession(session);
}
}


 [b][color=red]外联接：能够查出2个表之间不相互关联的记录[/color][/b]


 <PREclass=javaname="code"></PRE>
<BR>
 <BR>/**
<BR>*外联结
<BR>*/
 <BR>publicvoidtestQuery4(){
 <BR>Sessionsession=null;
 <BR>try{
<BR>session=HibernateUtils.getSession();
<BR>session.beginTransaction();
 <BR>//查询出所有的学生（包括没有班级的学生）
 <BR>Liststudents=session.createQuery("selects.name,c.namefromStudentsleftjoins.classesc").list();
 <BR>for(Iteratoriter=students.iterator();iter.hasNext();){
<BR>Object[]o=(Object[])iter.next();
 <BR>System.out.println("id="+o[0]+",o[1]="+o[1]);
<BR>}
<BR>session.getTransaction().commit();
 <BR>}catch(Exceptione){
<BR>e.printStackTrace();
<BR>session.getTransaction().rollback();
 <BR>}finally{
<BR>HibernateUtils.closeSession(session);
<BR>}
<BR>}
<BR>
<BR>
<BR>
 <BR>/**
<BR>*外联结
<BR>*/
 <BR>publicvoidtestQuery5(){
 <BR>Sessionsession=null;
 <BR>try{
<BR>session=HibernateUtils.getSession();
<BR>session.beginTransaction();
 <BR>//查询出所有的班级，（包括没有学生的班级）
 <BR>Liststudents=session.createQuery("selects.name,c.namefromStudentsrightjoins.classesc").list();
 <BR>for(Iteratoriter=students.iterator();iter.hasNext();){
<BR>Object[]o=(Object[])iter.next();
 <BR>System.out.println("id="+o[0]+",o[1]="+o[1]);
<BR>}
<BR>session.getTransaction().commit();
 <BR>}catch(Exceptione){
<BR>e.printStackTrace();
<BR>session.getTransaction().rollback();
 <BR>}finally{
<BR>HibernateUtils.closeSession(session);
<BR>}
<BR>}
<BR>
<BR>
<BR>}