1 // HQL: Hibernate Query Language.
2 // 特点:
3 // >> 1,与SQL相似,SQL中的语法基本上都可以直接使用。
4 // >> 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。
5 // >> 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。
6 // >> 4,SELECT可以省略.
7
8 // 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)
9 hql = "FROM Employee";
10 hql = "FROM Employee AS e"; // 使用别名
11 hql = "FROM Employee e"; // 使用别名,as关键字可省略
12
13 // 2,带上过滤条件的(可以使用别名):Where
14 hql = "FROM Employee WHERE id<10";
15 hql = "FROM Employee e WHERE e.id<10";
16 hql = "FROM Employee e WHERE e.id<10 AND e.id>5";
17
18 // 3,带上排序条件的:Order By
19 hql = "FROM Employee e WHERE e.id<10 ORDER BY e.name";
20 hql = "FROM Employee e WHERE e.id<10 ORDER BY e.name DESC";
21 hql = "FROM Employee e WHERE e.id<10 ORDER BY e.name DESC, id ASC";
22
23 // 4,指定select子句(不可以使用select *)
24 hql = "SELECT e FROM Employee e"; // 相当于"FROM Employee e"
25 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
26 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
27 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
28
29 // 5,执行查询,获得结果(list、uniqueResult、分页 )
30 Query query = session.createQuery("FROM Employee e WHERE id<3");
31 query.setFirstResult(0);
32 query.setMaxResults(10); // 等同于 limit 0,10
33 //两种查询结果list、uniqueResult
34 // List list = query.list(); // 查询的结果是一个List集合
35 // 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
36
37 // 6,方法链
38 List list = session.createQuery(//
39 "FROM Employee e")//
40 .setFirstResult(0)//
41 .setMaxResults(10)//
42 .list();
43
44 // 7,聚集函数:count(), max(), min(), avg(), sum()
45 hql = "SELECT COUNT(*) FROM Employee"; // 返回的结果是Long型的
46 hql = "SELECT min(id) FROM Employee"; // 返回的结果是id属性的类型
47
48 //8,分组: Group By ... Having
49 hql = "SELECT e.name,COUNT(e.id) FROM Employee e GROUP BY e.name";
50 hql = "SELECT e.name,COUNT(e.id) FROM Employee e GROUP BY e.name HAVING count(e.id)>1";
51 hql = "SELECT e.name,COUNT(e.id) FROM Employee e WHERE id<9 GROUP BY e.name HAVING count(e.id)>1";
52 hql = "SELECT e.name,COUNT(e.id) " + //
53 "FROM Employee e " + //
54 "WHERE id<9 " + //
55 "GROUP BY e.name " + //
56 "HAVING count(e.id)>1 " + //
57 "ORDER BY count(e.id) ASC";
58 hql = "SELECT e.name,COUNT(e.id) AS c " + //
59 "FROM Employee e " + //
60 "WHERE id<9 " + //
61 "GROUP BY e.name " + //
62 "HAVING count(e.id)>1 " + // 在having子句中不能使用列别名
63 "ORDER BY c ASC"; // 在orderby子句中可以使用列别名
64
65 // 9,连接查询 / HQL是面向对象的查询
66 //>> 内连接(inner关键字可以省略)
67 hql = "SELECT e.id,e.name,d.name FROM Employee e JOIN e.department d";
68 hql = "SELECT e.id,e.name,d.name FROM Employee e INNER JOIN e.department d";
69 //>> 左外连接(outer关键字可以省略)
70 hql = "SELECT e.id,e.name,d.name FROM Employee e LEFT OUTER JOIN e.department d";
71 //>> 右外连接(outer关键字可以省略)
72 hql = "SELECT e.id,e.name,d.name FROM Employee e RIGHT JOIN e.department d";
73 //可以使用更方便的方法
74 hql = "SELECT e.id,e.name,e.department.name FROM Employee e";
75
76 // 10,查询时使用参数
77 // >> 方式一:使用'?'占位
78 hql = "FROM Employee e WHERE id BETWEEN ? AND ?";
79 List list2 = session.createQuery(hql)//
80 .setParameter(0, 5)// 设置参数,第1个参数的索引为0。
81 .setParameter(1, 15)//
82 .list();
83
84 // >> 方式二:使用变量名
85 hql = "FROM Employee e WHERE id BETWEEN :idMin AND :idMax";
86 List list3 = session.createQuery(hql)//
87 .setParameter("idMax", 15)//
88 .setParameter("idMin", 5)//
89 .list();
90
91 // 当参数是集合时,一定要使用setParameterList()设置参数值
92 hql = "FROM Employee e WHERE id IN (:ids)";
93 List list4 = session.createQuery(hql)//
94 .setParameterList("ids", new Object[] { 1, 2, 3, 5, 8, 100 })//
95 .list();
96
97 // 11,update与delete,不会通知Session缓存
98 // >> Update
99 int result = session.createQuery(//
100 "UPDATE Employee e SET e.name=? WHERE id>15")//
101 .setParameter(0, "无名氏")//
102 .executeUpdate(); // 返回int型的结果,表示影响了多少行。
103 // >> Delete
104 int result1 = session.createQuery(//
105 "DELETE FROM Employee e WHERE id>15")//
106 .executeUpdate(); // 返回int型的结果,表示影响了多少行。