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>}