hql 语法与详细解释
// HQL: Hibernate Query Language. // 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):Where hql = "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 By hql = "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 ... Having hql = "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 // >> Update int 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。 // >> Delete int 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。
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作者:Honey_Badger —— 觉得这文章好,点一下左下角
出处:http://tk55.cnblogs.com/
posted on 2016-10-23 23:36 Honey_Badger 阅读(396) 评论(0) 编辑 收藏 举报