Hibernate 常用HQL語句

HQL: Hibernate Query Language.

HQL特點：
1，與SQL相似，SQL中的語法基本上都可以直接使用。
2，SQL查詢的是表和表中的列；HQL查詢的是對象與對象中的屬性。
3，HQL的關鍵字不區分大小寫，類名與屬性名是區分大小寫的。
4，SELECT可以省略。

1，簡單的查詢，Employee爲實體名而不是數據庫中的表名(面向對象特性)

hql = "FROM Employee";  
hql = "FROM Employee as e"; // 使用別名  
hql = "FROM Employee e"; // 使用別名，as關鍵字可省略  

2，帶上過濾條件的（可以使用別名）：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，帶上排序條件的：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"; // 相當於"FROM Employee e"  
hql = "SELECT e.name FROM Employee e"; // 只查詢一個列，返回的集合的元素類型就是這個屬性的類型  
hql = "SELECT e.id,e.name FROM Employee e"; // 查詢多個列，返回的集合的元素類型是Object數組  
hql = "SELECT new Employee(e.id,e.name) FROM Employee e"; // 可以使用new語法，指定把查詢出的部分屬性封裝到對象中

5，執行查詢，獲得結果（list、uniqueResult、分頁 ）

Query query = session.createQuery("FROM Employee e WHERE id<3");  
query.setFirstResult(0);  
query.setMaxResults(10); // 等同於 limit 0,10  
//兩種查詢結果list、uniqueResult  
List list = query.list(); // 查詢的結果是一個List集合  
Employee employee = (Employee) query.uniqueResult();// 查詢的結果是唯一的一個結果，當結果有多個，就會拋異常

6，方法鏈

List list = session.createQuery( 
        "FROM Employee e")
        .setFirstResult(0) 
        .setMaxResults(10)  
        .list(); 

7，聚集函數：count(), max(), min(), avg(), sum()

hql = "SELECT COUNT(*) FROM Employee"; // 返回的結果是Long型的  
hql = "SELECT min(id) FROM Employee"; // 返回的結果是id屬性的類型 

8，分組: 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子句中不能使用列別名  
     "ORDER BY c ASC"; // 在orderby子句中可以使用列別名

9，連接查詢 / HQL是面向對象的查詢

 // 內連接（inner關鍵字可以省略）  
 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";  
 // 左外連接（outer關鍵字可以省略）  
 hql = "SELECT e.id,e.name,d.name FROM Employee e LEFT OUTER JOIN e.department d";  
 // 右外連接（outer關鍵字可以省略）  
 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，查詢時使用參數

 //  方式一：使用'?'佔位  
 hql = "FROM Employee e WHERE id BETWEEN ? AND ?";  
 List list2 = session.createQuery(hql) 
     .setParameter(0, 5)// 設置參數，第1個參數的索引爲0。  
     .setParameter(1, 15)
     .list();  

 //  方式二：使用變量名  
 hql = "FROM Employee e WHERE id BETWEEN :idMin AND :idMax";  
 List list3 = session.createQuery(hql)  
     .setParameter("idMax", 15) 
     .setParameter("idMin", 5)  
     .list();  

 //  當參數是集合時，一定要使用setParameterList()設置參數值  
 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與delete，不會通知Session緩存

// >> Update  
int result = session.createQuery(  
        "UPDATE Employee e SET e.name=? WHERE id>15")  
        .setParameter(0, "無名氏")  
        .executeUpdate(); // 返回int型的結果，表示影響了多少行。  
// >> Delete  
int result1 = session.createQuery(  
        "DELETE FROM Employee e WHERE id>15")  
        .executeUpdate(); 返回int型的結果，表示影響了多少行。

本文是轉載的，出處:http://blog.csdn.net/v123411739/article/details/28644007