📅 最后修改于: 2020-11-13 04:42:22 🧑 作者: Mango
本章提供了有关如何使用JDBC应用程序对表中的记录进行排序的示例。这将使用asc和desc关键字对记录进行升序或降序排序。在执行以下示例之前，请确保已具备以下条件：
要执行以下示例，您可以将用户名和密码替换为实际的用户名和密码。
您的MySQL或您正在使用的任何数据库均已启动并正在运行。
使用JDBC应用程序创建新数据库需要执行以下步骤-
导入软件包：要求您包含包含数据库编程所需的JDBC类的软件包。通常，使用import java.sql。*就足够了。
注册JDBC驱动程序：要求您初始化驱动程序，以便您可以打开与数据库的通信通道。
打开连接：需要使用DriverManager.getConnection()方法创建一个Connection对象，该对象表示与数据库服务器的物理连接。
执行查询：需要使用Statement类型的对象来构建和提交SQL语句以对表中的记录进行排序。这些查询使用asc和desc子句对数据进行升序和降序排序。
清理环境：需要显式关闭所有数据库资源，而不是依赖JVM的垃圾回收。
将以下示例复制并粘贴到JDBCExample.java中，编译并运行如下-
//STEP 1. Import required packages
import java.sql.*;
public class JDBCExample {
// JDBC driver name and database URL
static final String JDBC_DRIVER = "com.mysql.jdbc.Driver";
static final String DB_URL = "jdbc:mysql://localhost/STUDENTS";
// Database credentials
static final String USER = "username";
static final String PASS = "password";
public static void main(String[] args) {
Connection conn = null;
Statement stmt = null;
try{
//STEP 2: Register JDBC driver
Class.forName("com.mysql.jdbc.Driver");
//STEP 3: Open a connection
System.out.println("Connecting to a selected database...");
conn = DriverManager.getConnection(DB_URL, USER, PASS);
System.out.println("Connected database successfully...");
//STEP 4: Execute a query
System.out.println("Creating statement...");
stmt = conn.createStatement();
// Extract records in ascending order by first name.
System.out.println("Fetching records in ascending order...");
String sql = "SELECT id, first, last, age FROM Registration" +
" ORDER BY first ASC";
ResultSet rs = stmt.executeQuery(sql);
while(rs.next()){
//Retrieve by column name
int id = rs.getInt("id");
int age = rs.getInt("age");
String first = rs.getString("first");
String last = rs.getString("last");
//Display values
System.out.print("ID: " + id);
System.out.print(", Age: " + age);
System.out.print(", First: " + first);
System.out.println(", Last: " + last);
}
// Extract records in descending order by first name.
System.out.println("Fetching records in descending order...");
sql = "SELECT id, first, last, age FROM Registration" +
" ORDER BY first DESC";
rs = stmt.executeQuery(sql);
while(rs.next()){
//Retrieve by column name
int id = rs.getInt("id");
int age = rs.getInt("age");
String first = rs.getString("first");
String last = rs.getString("last");
//Display values
System.out.print("ID: " + id);
System.out.print(", Age: " + age);
System.out.print(", First: " + first);
System.out.println(", Last: " + last);
}
rs.close();
}catch(SQLException se){
//Handle errors for JDBC
se.printStackTrace();
}catch(Exception e){
//Handle errors for Class.forName
e.printStackTrace();
}finally{
//finally block used to close resources
try{
if(stmt!=null)
conn.close();
}catch(SQLException se){
}// do nothing
try{
if(conn!=null)
conn.close();
}catch(SQLException se){
se.printStackTrace();
}//end finally try
}//end try
System.out.println("Goodbye!");
}//end main
}//end JDBCExample
现在，让我们编译上面的示例，如下所示：
C:\>javac JDBCExample.java
C:\>
当您运行JDBCExample时，它将产生以下结果-
C:\>java JDBCExample
Connecting to a selected database...
Connected database successfully...
Creating statement...
Fetching records in ascending order...
ID: 103, Age: 28, First: Sumit, Last: Mittal
ID: 102, Age: 30, First: Zaid, Last: Khan
ID: 100, Age: 30, First: Zara, Last: Ali
Fetching records in descending order...
ID: 100, Age: 30, First: Zara, Last: Ali
ID: 102, Age: 30, First: Zaid, Last: Khan
ID: 103, Age: 28, First: Sumit, Last: Mittal
Goodbye!
C:\>