Java连接数据库,多表查询

Java以编程的形式连接数据库，并实现多表查询，查询条件是三年级2班，语文成绩大于80分的学生，并打出名单。代码如下：

package Public;

import java.sql.*;

//建立类Conn，连接MySQL数据库，数据库多表查询。

public class Conn {

public static void main(String[] args) {

//声明Connection对象

Connection con;

// 数据库驱动

String DRIVER = "com.mysql.jdbc.Driver";

// 3306后面为数据库名字测试时可以删除

String url = "jdbc:mysql://localhost:3306/stu_glxt";

String username = "root";

// 数据库密码

String password ="123456" ;

try {

// 注册驱动

Class.forName(DRIVER);

//1.getConnection()方法，连接MySQL数据库！！

con = DriverManager.getConnection(url, username, password);

if(!con.isClosed())

System.out.println("Succeeded connecting to the Database!");

//2.创建statement类对象，用来执行SQL语句！！

Statement statement = con.createStatement();

//要执行的SQL语句，查询三年级2班语文成绩大于80分的学生 String sql = "select A.sName,

B.score,

ame,

D.sGrade,D.sClass" +

" from tb_student AS A,tb_score AS B,tb_course AS C,tb_grade AS D " +

" where A.sNo=B.sNo and o=o and

A.sNo=D.sNo and " +

" D.sGrade='三年级' and D.sClass=2 and

o=000002 and B.score>=80";

//3.ResultSet类，用来存放获取的结果集！！

ResultSet rs = statement.executeQuery(sql); System.out.println("----------------------------------");

System.out.println("执行结果如下所示:");

System.out.println("----------------------------------");

System.out.println(" 姓名" + "\t" + " 分数"+"\t"+"课程名"+"\t"+"年级"+"\t"+"班级");

System.out.println("----------------------------------");

String sName = null;

String score = null;

String cName= null;

String grade = null;

String sclass = null;

while(rs.next()){

//获取sName这列数据

sName = rs.getString("sName");

//获取sNo这列数据

score = rs.getString("score");

cName = rs.getString("cName");

grade = rs.getString("sGrade");

sclass = rs.getString("sClass");

//输出结果

System.out.println(sName + "\t" +

score+"\t"+cName+"\t"+grade+"\t"+ sclass);

}

rs.close();

con.close();

} catch(ClassNotFoundException e) {

//数据库驱动类异常处理

System.out.println("Sorry,can`t find the Driver!");

e.printStackTrace();

} catch(SQLException e) {

//数据库连接失败异常处理

e.printStackTrace();

}catch (Exception e) {

// TODO: handle exception

e.printStackTrace();

}finally{

System.out.println("数据库数据成功获取！！");

}

}

}