常用HQL语句

最近学习Hibernate，因此总结了一些常用HQL语句

 特点： >> 1，与SQL相似，SQL中的语法基本上都可以直接使用。 >> 2，SQL查询的是表和表中的列；HQL查询的是对象与对象中的属性。 >> 3，HQL的关键字不区分大小写，类名与属性名是区分大小写的。 >> 4，SELECT可以省略.        1，简单的查询，Employee为实体名而不是数据库中的表名(面向对象特性)hql = "FROM Employee";hql = "FROM Employee AS e";  //使用别名hql = "FROM Employee e";  //使用别名，as关键字可省略 2，带上过滤条件的（可以使用别名）：Wherehql = "FROM Employee WHERE id<10";hql = "FROM Employee e WHERE e.id<10";hql = "FROM Employee e WHERE e.id<10 AND e.id>5"; 3，带上排序条件的：Order Byhql = "FROM Employee e WHERE e.id<10 ORDER BY e.name";hql = "FROM Employee e WHERE e.id<10 ORDER BY e.name DESC";hql = "FROM Employee e WHERE e.id<10 ORDER BY e.name DESC, id ASC"; 4，指定select子句（不可以使用select *）hql = "SELECT e FROM Employee e";  //相当于"FROM Employee e"hql = "SELECT e.name FROM Employee e";  //只查询一个列，返回的集合的元素类型就是这个属性的类型hql = "SELECT e.id,e.name FROM Employee e"; // 查询多个列，返回的集合的元素类型是Object数组hql = "SELECT new Employee(e.id,e.name) FROM Employee e";  //可以使用new语法，指定把查询出的部分属性封装到对象中 5，执行查询，获得结果（list、uniqueResult、分页 ）Query query = session.createQuery("FROM Employee e WHERE id<3");query.setFirstResult(0);query.setMaxResults(10);  //等同于 limit 0,10两种查询结果list、uniqueResult List list = query.list();  //查询的结果是一个List集合 Employee employee = (Employee) query.uniqueResult(); //查询的结果是唯一的一个结果，当结果有多个，就会抛异常 6，方法链List list = session.createQuery(        "FROM Employee e")        .setFirstResult(0)        .setMaxResults(10)        .list(); 7，聚集函数：count(), max(), min(), avg(), sum()hql = "SELECT COUNT(*) FROM Employee";  //返回的结果是Long型的hql = "SELECT min(id) FROM Employee";  //返回的结果是id属性的类型8，分组: Group By ... Havinghql = "SELECT e.name,COUNT(e.id) FROM Employee e GROUP BY e.name";hql = "SELECT e.name,COUNT(e.id) FROM Employee e GROUP BY e.name HAVING count(e.id)>1";hql = "SELECT e.name,COUNT(e.id) FROM Employee e WHERE id<9 GROUP BY e.name HAVING count(e.id)>1";hql = "SELECT e.name,COUNT(e.id) " +      "FROM Employee e " +      "WHERE id<9 " +      "GROUP BY e.name " +      "HAVING count(e.id)>1 " +      "ORDER BY count(e.id) ASC";hql = "SELECT e.name,COUNT(e.id) AS c " +      "FROM Employee e " +      "WHERE 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orderby子句中可以使用列别名 9，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关键字可以省略） hql = "SELECT e.id,e.name,d.name FROM Employee e LEFT OUTER JOIN e.department d"; >> 右外连接（outer关键字可以省略） hql = "SELECT e.id,e.name,d.name FROM Employee e RIGHT JOIN e.department d"; 可以使用更方便的方法 hql = "SELECT e.id,e.name,e.department.name FROM Employee e"; 10，查询时使用参数 >> 方式一：使用'?'占位 hql = "FROM Employee e WHERE id BETWEEN ? AND ?"; List list2 = 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 id BETWEEN :idMin AND :idMax"; List list3 = session.createQuery(hql)     .setParameter("idMax", 15)     .setParameter("idMin", 5)     .list(); //当参数是集合时，一定要使用setParameterList()设置参数值 hql = "FROM Employee e WHERE id IN (:ids)"; List list4 = session.createQuery(hql)     .setParameterList("ids", new Object[] { 1, 2, 3, 5, 8, 100 })     .list(); 11，update与delete，不会通知Session缓存 >> Updateint result = session.createQuery(        "UPDATE Employee e SET e.name=? WHERE id>15")        .setParameter(0, "无名氏")        .executeUpdate();   //返回int型的结果，表示影响了多少行 >> Deleteint result1 = session.createQuery(        "DELETE FROM Employee e WHERE id>15")        .executeUpdate();   // 返回int型的结果，表示影响了多少行。