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hql常用查询语句

hql常用查询语句

// 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。
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