我需要你的帮助。我不知道为什么我的代码没有更新数据,即使我使用了正确的代码和正确的数据输入。我希望你能帮助我。这是为了我的任务。谢谢!
顺便说一句,这是我的代码:
包分配;
import java.sql.*;
import java.util.Scanner;
public class assignment_prepared {
public static void main(String[] args) throws SQLException{
updateTable();
}
private static void updateTable() throws SQLException{
Connection conn= DriverManager.getConnection("jdbc:mysql://localhost:3306/studentdatabase", "root", "password");
PreparedStatement preparedStatement2 =null;
String UpdateSQL= "Update studentrecord set lastname = ? where studentid = ?";
try{
preparedStatement2 =conn.prepareStatement(UpdateSQL);
Scanner scan =new Scanner(System.in);
System.out.println("Updating...");
System.out.println("Enter StudentId: ");
int studentid=scan.nextInt();
System.out.println("Enter Lastname: ");
String lastname=scan.next();
preparedStatement2.setInt(1, studentid);
preparedStatement2.setString(2, lastname);
preparedStatement2.executeUpdate();
ResultSet myRs2= preparedStatement2.executeQuery("Select * from studentrecord");
while(myRs2.next() ){
System.out.println(myRs2.getInt("studentid") + " " +myRs2.getString("lastname") + " " +
myRs2.getString("firstname") + " " +myRs2.getInt("tfee") + " " +myRs2.getDouble("fee_per_unit") +
" " +myRs2.getInt("total_unit") + " " +myRs2.getString("year") + " " +myRs2.getString("course")
+ " " +myRs2.getString("section"));
}
}catch(Exception exc){
exc.printStackTrace();
}
}
}
最佳答案
您颠倒了参数:
Update studentrecord set lastname = ? where studentid = ?
↑ ↑
1 2
但是你写道:
preparedStatement2.setInt(1, studentid);
preparedStatement2.setString(2, lastname);
什么时候应该是:
preparedStatement2.setString(1, lastname);
preparedStatement2.setInt(2, studentid);
<小时/>
除此之外,您应该将 JDBC 代码与用户提示代码隔离,并且应该使用 try-with-resources,因为您当前正在泄漏资源(严重)。
private static void updateTable() {
try {
Scanner scan =new Scanner(System.in);
System.out.println("Updating...");
System.out.println("Enter StudentId: ");
int studentid=scan.nextInt();
System.out.println("Enter Lastname: ");
String lastname=scan.next();
try (Connection conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/studentdatabase", "root", "password")) {
updateTable(conn, studentid, lastname);
listRecords(conn);
}
} catch(Exception exc){
exc.printStackTrace();
}
}
private static void updateTable(Connection conn, int studentid, String lastname) throws SQLException {
String updateSQL = "UPDATE studentrecord SET lastname = ? WHERE studentid = ?";
try (PreparedStatement stmt = conn.prepareStatement(updateSQL)) {
stmt.setString(1, lastname);
stmt.setInt(2, studentid);
stmt.executeUpdate();
}
}
private static void listRecords(Connection conn) throws SQLException {
String selectSQL = "SELECT * FROM studentrecord";
try (
Statement stmt = conn.createStatement();
ResultSet rs = stmt.executeQuery(selectSQL)
) {
while (rs.next()) {
System.out.println(rs.getInt("studentid") + " " +
rs.getString("lastname") + " " +
rs.getString("firstname") + " " +
rs.getInt("tfee") + " " +
rs.getDouble("fee_per_unit") + " " +
rs.getInt("total_unit") + " " +
rs.getString("year") + " " +
rs.getString("course") + " " +
rs.getString("section"));
}
}
}
关于java - 使用准备好的语句和用户输入更新数据,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/38944219/