常用的Hql语句
// 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。