内连接，迫切内连接，左外连接，迫切左外连接

        内连接：

     查询出来的每一项为 object[]数组，左表存在object[0]中，右表存在object[1]中，object[0]和object[1]的关联关系有没有设置，取决于你的配置文件中，关联的配置时候lazy的值，如果lazy=false，则马上维护关系，lazy=true，先不维护关系，等用到关联关系维系的值时才查询。

    Session session = DBUtil.getSession();        String hql = "from Deptment d inner join d.employees";        Query query = session.createQuery(hql);        //如果设置lazy=”false",这时候就会关联部门和员工，除了发送内连接语句外，还发送了查询每个        //部门下有哪些员工的sql语句        List list = query.list();        Iterator iter = list.iterator();        while(iter.hasNext())        {        Object[] object = (Object[]) iter.next();        System.out.println("部门信息:");        System.out.println(object[0]);                Deptment dept = (Deptment)object[0];        //如果设置lazy="true"的时候，这时候才去查询部门的员工，发sql语句        System.out.println(dept.getEmployees());        System.out.println("员工信息:");        System.out.println(object[1]);        }        session.close();

   结果1(设置关联关系的维护为lazy=true）：

   

Hibernate:     select        deptment0_.deptid as deptid0_0_,        employees1_.epno as epno1_1_,        deptment0_.deptname as deptname0_0_,        employees1_.deptid as deptid1_1_,        employees1_.epname as epname1_1_     from        deptment deptment0_     inner join        employee employees1_             on deptment0_.deptid=employees1_.deptid部门信息:Deptment [deptid=1, deptname=aaa]Hibernate:     select        employees0_.deptid as deptid1_,        employees0_.epno as epno1_,        employees0_.epno as epno1_0_,        employees0_.deptid as deptid1_0_,        employees0_.epname as epname1_0_     from        employee employees0_     where        employees0_.deptid=?[Employee [epno=2, deptment=Deptment [deptid=1, deptname=aaa], epname=shizhan2], Employee [epno=1, deptment=Deptment [deptid=1, deptname=aaa], epname=null]]员工信息:Employee [epno=1, deptment=Deptment [deptid=1, deptname=aaa], epname=null]部门信息:Deptment [deptid=1, deptname=aaa][Employee [epno=2, deptment=Deptment [deptid=1, deptname=aaa], epname=shizhan2], Employee [epno=1, deptment=Deptment [deptid=1, deptname=aaa], epname=null]]员工信息:Employee [epno=2, deptment=Deptment [deptid=1, deptname=aaa], epname=shizhan2]部门信息:Deptment [deptid=3, deptname=sdsdzz]Hibernate:     select        employees0_.deptid as deptid1_,        employees0_.epno as epno1_,        employees0_.epno as epno1_0_,        employees0_.deptid as deptid1_0_,        employees0_.epname as epname1_0_     from        employee employees0_     where        employees0_.deptid=?[Employee [epno=3, deptment=Deptment [deptid=3, deptname=sdsdzz], epname=xsxs], Employee [epno=4, deptment=Deptment [deptid=3, deptname=sdsdzz], epname=ttt]]员工信息:Employee [epno=3, deptment=Deptment [deptid=3, deptname=sdsdzz], epname=xsxs]部门信息:Deptment [deptid=3, deptname=sdsdzz][Employee [epno=3, deptment=Deptment [deptid=3, deptname=sdsdzz], epname=xsxs], Employee [epno=4, deptment=Deptment [deptid=3, deptname=sdsdzz], epname=ttt]]员工信息:Employee [epno=4, deptment=Deptment [deptid=3, deptname=sdsdzz], epname=ttt]

  结果2（设置关联关系的维护lazy=false，关联关系立马维护，产生多条sql语句）

  

Hibernate:     select        deptment0_.deptid as deptid0_0_,        employees1_.epno as epno1_1_,        deptment0_.deptname as deptname0_0_,        employees1_.deptid as deptid1_1_,        employees1_.epname as epname1_1_     from        deptment deptment0_     inner join        employee employees1_             on deptment0_.deptid=employees1_.deptidHibernate:     select        employees0_.deptid as deptid1_,        employees0_.epno as epno1_,        employees0_.epno as epno1_0_,        employees0_.deptid as deptid1_0_,        employees0_.epname as epname1_0_     from        employee employees0_     where        employees0_.deptid=?Hibernate:     select        employees0_.deptid as deptid1_,        employees0_.epno as epno1_,        employees0_.epno as epno1_0_,        employees0_.deptid as deptid1_0_,        employees0_.epname as epname1_0_     from        employee employees0_     where        employees0_.deptid=?部门信息:Deptment [deptid=1, deptname=aaa][Employee [epno=2, deptment=Deptment [deptid=1, deptname=aaa], epname=shizhan2], Employee [epno=1, deptment=Deptment [deptid=1, deptname=aaa], epname=null]]员工信息:Employee [epno=1, deptment=Deptment [deptid=1, deptname=aaa], epname=null]部门信息:Deptment [deptid=1, deptname=aaa][Employee [epno=2, deptment=Deptment [deptid=1, deptname=aaa], epname=shizhan2], Employee [epno=1, deptment=Deptment [deptid=1, deptname=aaa], epname=null]]员工信息:Employee [epno=2, deptment=Deptment [deptid=1, deptname=aaa], epname=shizhan2]部门信息:Deptment [deptid=3, deptname=sdsdzz][Employee [epno=3, deptment=Deptment [deptid=3, deptname=sdsdzz], epname=xsxs], Employee [epno=4, deptment=Deptment [deptid=3, deptname=sdsdzz], epname=ttt]]员工信息:Employee [epno=3, deptment=Deptment [deptid=3, deptname=sdsdzz], epname=xsxs]部门信息:Deptment [deptid=3, deptname=sdsdzz][Employee [epno=3, deptment=Deptment [deptid=3, deptname=sdsdzz], epname=xsxs], Employee [epno=4, deptment=Deptment [deptid=3, deptname=sdsdzz], epname=ttt]]员工信息:Employee [epno=4, deptment=Deptment [deptid=3, deptname=sdsdzz], epname=ttt]

   迫切内连接（不管设置lazy=true或者lazy=false，他关联关系立马就维护好了，且只发送一条sql语句，且结果集中的每条结果为 对象（本例中为部门对象，部门里面的员工已经填充好了）

   

 Session session = DBUtil.getSession();         String hql = "from Deptment d inner join fetch d.employees";         Query query = session.createQuery(hql);         List list = query.list();         Iterator iter = list.iterator();         while(iter.hasNext())         {         Deptment object = (Deptment) iter.next();         System.out.println("部门信息:");         System.out.println(object);         System.out.println("员工信息:");         System.out.println(object.getEmployees());         }

   结果：

   

Hibernate:     select        deptment0_.deptid as deptid0_0_,        employees1_.epno as epno1_1_,        deptment0_.deptname as deptname0_0_,        employees1_.deptid as deptid1_1_,        employees1_.epname as epname1_1_,        employees1_.deptid as deptid0__,        employees1_.epno as epno0__     from        deptment deptment0_     inner join        employee employees1_             on deptment0_.deptid=employees1_.deptid部门信息:Deptment [deptid=1, deptname=aaa]员工信息:[Employee [epno=2, deptment=Deptment [deptid=1, deptname=aaa], epname=shizhan2], Employee [epno=1, deptment=Deptment [deptid=1, deptname=aaa], epname=null]]部门信息:Deptment [deptid=1, deptname=aaa]员工信息:[Employee [epno=2, deptment=Deptment [deptid=1, deptname=aaa], epname=shizhan2], Employee [epno=1, deptment=Deptment [deptid=1, deptname=aaa], epname=null]]部门信息:Deptment [deptid=3, deptname=sdsdzz]员工信息:[Employee [epno=3, deptment=Deptment [deptid=3, deptname=sdsdzz], epname=xsxs], Employee [epno=4, deptment=Deptment [deptid=3, deptname=sdsdzz], epname=ttt]]部门信息:Deptment [deptid=3, deptname=sdsdzz]员工信息:[Employee [epno=3, deptment=Deptment [deptid=3, deptname=sdsdzz], epname=xsxs], Employee [epno=4, deptment=Deptment [deptid=3, deptname=sdsdzz], epname=ttt]]

   左外连接：在内连接的基础上，保证左表的数据不能丢失，如果左表中没有对应的右表数据，则右表对象置为空。lazy的设置导致的结果影响和内连接相同。

   代码：

   

   Session session = DBUtil.getSession();        String hql = "from Deptment d left join d.employees";        Query query = session.createQuery(hql);        List list = query.list();        Iterator iter = list.iterator();        while(iter.hasNext())        {        Object[] object = (Object[]) iter.next();        System.out.println("部门信息:");        System.out.println(object[0]);        System.out.println("员工信息:");        if(object[1]!=null){           System.out.println(object[1]);        }else{       System.out.println("null");        }        }        session.close();

    结果（lazy=true 的时候），我们可以看到最后多了一个null：

   

Hibernate:     select        deptment0_.deptid as deptid0_0_,        employees1_.epno as epno1_1_,        deptment0_.deptname as deptname0_0_,        employees1_.deptid as deptid1_1_,        employees1_.epname as epname1_1_     from        deptment deptment0_     left outer join        employee employees1_             on deptment0_.deptid=employees1_.deptid部门信息:Deptment [deptid=1, deptname=aaa]员工信息:Employee [epno=1, deptment=Deptment [deptid=1, deptname=aaa], epname=null]部门信息:Deptment [deptid=1, deptname=aaa]员工信息:Employee [epno=2, deptment=Deptment [deptid=1, deptname=aaa], epname=shizhan2]部门信息:Deptment [deptid=3, deptname=sdsdzz]员工信息:Employee [epno=3, deptment=Deptment [deptid=3, deptname=sdsdzz], epname=xsxs]部门信息:Deptment [deptid=3, deptname=sdsdzz]员工信息:Employee [epno=4, deptment=Deptment [deptid=3, deptname=sdsdzz], epname=ttt]部门信息:Deptment [deptid=2, deptname=aaa]员工信息:null

  迫切左外连接：

  

     Session session = DBUtil.getSession();       String hql = "from Deptment d left join fetch d.employees";       Query query = session.createQuery(hql);       List list = query.list();       Iterator iter = list.iterator();       while(iter.hasNext())       {       Deptment object = (Deptment) iter.next();       System.out.println("部门信息:");       System.out.println(object);       System.out.println("员工信息:");       System.out.println(object.getEmployees());       }

   结果：

  

Hibernate:     select        deptment0_.deptid as deptid0_0_,        employees1_.epno as epno1_1_,        deptment0_.deptname as deptname0_0_,        employees1_.deptid as deptid1_1_,        employees1_.epname as epname1_1_,        employees1_.deptid as deptid0__,        employees1_.epno as epno0__     from        deptment deptment0_     left outer join        employee employees1_             on deptment0_.deptid=employees1_.deptid部门信息:Deptment [deptid=1, deptname=aaa]员工信息:[Employee [epno=2, deptment=Deptment [deptid=1, deptname=aaa], epname=shizhan2], Employee [epno=1, deptment=Deptment [deptid=1, deptname=aaa], epname=null]]部门信息:Deptment [deptid=1, deptname=aaa]员工信息:[Employee [epno=2, deptment=Deptment [deptid=1, deptname=aaa], epname=shizhan2], Employee [epno=1, deptment=Deptment [deptid=1, deptname=aaa], epname=null]]部门信息:Deptment [deptid=3, deptname=sdsdzz]员工信息:[Employee [epno=3, deptment=Deptment [deptid=3, deptname=sdsdzz], epname=xsxs], Employee [epno=4, deptment=Deptment [deptid=3, deptname=sdsdzz], epname=ttt]]部门信息:Deptment [deptid=3, deptname=sdsdzz]员工信息:[Employee [epno=3, deptment=Deptment [deptid=3, deptname=sdsdzz], epname=xsxs], Employee [epno=4, deptment=Deptment [deptid=3, deptname=sdsdzz], epname=ttt]]部门信息:Deptment [deptid=2, deptname=aaa]员工信息:[]