连接分为内连接、外连接和全连接
外连接分为：左外连接、右连接
内连接又叫自然连接
createQuery()的括号里面不能写select * .
mySQL不支持full join
inner join(等值连接)：只返回两个表中连结字段相等的行
left join(左连接)：返回包括左表中的所有记录和右表中连结字段相等的记录
A表 left join B表 左连 以A表位基础，A表的全部数据，B表有的组合，没有的为null
right join(右连接)：返回包括右表的所有记录和左表中连结字段相等的记录
A表 right join B表 右连 以B表位基础，B表的全部数据，A表有的组合，没有的为null
select c.*,o.* from customers c,orders owhere c.id=o.cid全连接
select c.*,o.* from customers c INNER joinorders o on c.id=o.cid等值内连接
select c.*,o.* from customers c LEFT joinorders o on c.id=o.cid左外连接
//连接查询
//内连接
@Test
public void join2(){
Session session=HibernateUtil.getSession();
// select c.id,c.realName,o.id,o.number fromCustomers as c left join c.orders as o where c.id=1
List<Object[]> customer=session.createQuery("select c.id,c.realName,o.id,o.number from Customersas c left join c.orders as o where c.id=1").list();
for(Object[] c:customer){
System.out.println(c[0]+"----"+c[1]);
}
}
运行后结果：
Hibernate: selectcustomers0_.id as col_0_0_, customers0_.realName as col_1_0_, orders1_.id ascol_2_0_, orders1_.number as col_3_0_ from pros.customers customers0_ leftouter join pros.Orders orders1_ on customers0_.id=orders1_.cid wherecustomers0_.id=1
1----435
//Criteria方法查询
@Test
public void join3(){
Session session=HibernateUtil.getSession();
/*Criteria criteria=session.createCriteria(Customers.class).add(Restrictions.like("realName","%a%"));//返回的是Criteria对象
List<Customers> customers=criteria.list();*/
List<Customers> customers=session.createCriteria(Customers.class)
.add(Restrictions.like("realName", "%a%"))
.createCriteria("orders")
.add(Restrictions.like("number", "%223%"))
.list();//链式查询
for(Customers c:customers){
System.out.println(c.getEmail());
}
}
//标量查询
@Test
public void join4(){
Session session=HibernateUtil.getSession();
//session.createSQLQuery("select* from customers").list();默认返回的是数组
List<Customers> customers=session.createSQLQuery("select * from customers").addEntity(Customers.class).list();//加了.addEntity(Customers.class)，返回的就不是数组而是实体对象了
for(Customers c:customers){
System.out.println(c.getEmail());
}
}