hibernate——HQL查询总结

hibernate——HQL查询总结

• HQL概述:
• HQL的简单查询
• HQL的别名查询:
• HQL的多态查询:
• HQL的排序查询:
• HQL的分页查询:
• HQL检索单个对象:
• HQL的条件查询:
• HQL使用汇集函数:
• HQL分组统计:
• HQL的投影查询:

HQL概述:

HQL(Hibernate Query Language) 是面向对象的查询语言, 它和 SQL 查询语言有些类似. 在 Hibernate 提供的各类检索方式中, HQL 是使用最广的一种检索方式.

list ： 查询结果多个
uniqueResult ： 查询结果惟一

HQL的简单查询

// 简单查询:
String hql = "from Customer";
//方法一
Query query = session.createQuery(hql);
List<Customer> list = query.list();
//方法二
List<Customer> list = session.createQuery(hql).list();

HQL的别名查询:

// 别名查询:
//String hql = "from Customer asc";
//String hql = "from Customer c";
String hql = "select c from Customer c";

HQL的多态查询:

String hql = "from java.lang.Object";
String hql = "from java.io.Serializable";

HQL的排序查询:

String hql = "from Customer order by age asc";
String hql = "from Customer order by age desc";

HQL的分页查询:

Query query = session.createQuery("from Order");
query.setFirstResult(10);
query.setMaxResults(10);
List<Order> list = query.list();

HQL检索单个对象:

Query query = session.createQuery("from Customer where cname = ?");
query.setParameter(0, "张三");
Customer customer = (Customer) query.uniqueResult();

HQL的条件查询:

/** * HQL条件查询 * 按位置绑定参数: */
// 1.根据名称进行查询
List<Customer> list = session
		.createQuery(
				"from Customer where cname = ?")
		.setParameter(0,"张三").list(); 

System.out.println(list.get(0));

// 2.根据名称进行查询
List<Customer> list = session
		.createQuery(
				"from Customer c where c.cname = ?") 
		.setParameter(0,"张三").list(); 

System.out.println(list.get(0));

// 3.条件并列:
List<Customer> list = session
		.createQuery(
				"from Customer where cname like ? and age >= ?")
		.setParameter(0, "任%").setParameter(1, 35).list();

for (Customer customer : list) {
	System.out.println(customer);
}

/** * HQL条件查询 * 按名称绑定参数: */
List<Customer> list = session
		.createQuery(
				"from Customer where cname like :cname and age >= :age")
		.setParameter("cname", "任%").setParameter("age", 35).list();
		
for (Customer customer : list) {
	System.out.println(customer);
}

HQL使用汇集函数:

//count()/max()/min()/avg()/sum()
String hql = "select count(*) from Order";
Long num = (Long) session.createQuery(hql).uniqueResult();

HQL分组统计:

String hql = "select o.customer.cname,count(*) from Order o group by o.customer.cname";
List<Object[]> list = session.createQuery(hql).list();
for (Object[] objects : list) {
	System.out.println(Arrays.toString(objects));
}

HQL的投影查询:

String hql = "select cname from Customer";
List<String> list  = session.createQuery(hql).list();
for (String cname : list) {
	System.out.println(cname);
}
		
String hql = "select age from Customer";
List<Integer> list  = session.createQuery(hql).list();
for (Integer age : list) {
	System.out.println(age);
}

String hql= "select cname,age from Customer";
List<Object[]> list  = session.createQuery(hql).list();
for (Object[] objects : list) {
	System.out.println(Arrays.toString(objects));
}

// 使用构造函数的方式进行投影查询.
String hql = "select new Customer(cname,age) from Customer";
List<Customer> list = session.createQuery(hql).list();
for (Customer customer : list) {
	System.out.println(customer);
}