Hibernate_查询_HQL详解（二）_聚集函数、分组、连接查询、查询时使用参数的HQL语法

1，聚集函数2，分组3，连接查询 / HQL是面向对象的查询数据库中查询：select e.id_, e.name_, d.name_ from employee e inner join department d on e.departmentId=d.id_;(内连接)select e.id_, e.name_, d.name_ from employee e left outer join department d on e.departmentId=d.id_;(左外连接)select e.id_, e.name_, d.name_ from employee e right outer join department d on e.departmentId=d.id_;(右外连接)4，查询时使用参数>> 方式一：使用'?'占位>> 方式二：使用变量名

// 使用HQL查询@Testpublic void testHql2() throws Exception {Session session = sessionFactory.openSession();Transaction tx = null;try {tx = session.beginTransaction();// ------------------------------------String hql = null;//// 1，聚集函数：count(),max(),min(),avg(),sum()// 总数、最大、最小、平均、求和// hql = "select count(e) from Employee e";// 返回的结果是Long型的// hql = "select min(e.id) from Employee e";// 返回的结果是id的属性的类型// Long result = (Long) session.createQuery(hql).uniqueResult();// Number result = (Number) session.createQuery(hql).uniqueResult();// System.out.println("总记录数：" + result.intValue());// 2，分组：Group By ... Having// hql = "select e.name,count(*) from Employee e group by e.name";// hql = "select e.name,count(*) from Employee e group by e.name Having count(e.id)>1";// hql = "select e.name,count(*) from Employee e where e.id<9 group by e.name  Having count(e.id)>1";// hql = "select e.name,count(*) " + //// ---// "from Employee e " + //// "where e.id<9 " + //// "group by e.name  " + //// "Having count(e.id)>1 " + //// "order by count(e.id) asc";// ---// hql = "select e.name,count(*) as c " + //// "from Employee e " + //// "where e.id<9 " + //// "group by e.name  " + //// "Having count(e.id)>1 " + // 在Having子句中不能使用列别名// "Order by c asc";// 在Order by中可以使用列别名// 3，连接查询 / HQL是面向对象的查询// >> 内连接(inner关键字可以省略)// hql = "select e.id,e.name,d.name from Employee e join e.department d";// hql = "select e.id,e.name,d.name from Employee e inner join e.department d";// >> 左外连接(outer关键可以省略)// hql = "select e.id,e.name,d.name from Employee e left outer join e.department d";// >> 右外连接(outer关键可以省略)// hql = "select e.id,e.name,d.name from Employee e right outer join e.department d";// 可以使过更方便的方法// hql = "select e.id,e.name,e.department.name from Employee e";// 4，查询时使用参数// >> 方式一：使用'?'占位// hql = "from Employee e where e.id between ? And ?";// List<Object> list = session.createQuery(hql)//// .setParameter(0, 5)// 设置参数,第1个参数的索引为0。// .setParameter(1, 15)//// .list();// >> 方式二：使用变量名// hql = "from Employee e where e.id between :idMin And :idMax";// List<Object> list = session.createQuery(hql)//// .setParameter("idMin", 5)//// .setParameter("idMax", 15)//// .list();// >> 方式三：当参数是集合时,一定要使用ParameterList()设置参数值hql = "from Employee e where id in (:ids)";List<Object> list = session.createQuery(hql)//.setParameterList("ids", new Object[] { 1, 2, 3, 5, 8, 100 })//.list();// ------------------------------------// ------ 查询结果并 显示结果// List<Object> list = session.createQuery(hql).list();for (Object obj : list) {if (obj.getClass().isArray()) {System.out.println(Arrays.toString((Object[]) obj));} else {System.out.println(obj);}}tx.commit();} catch (RuntimeException e) {tx.rollback();throw e;} finally {session.close();}}