java - JDBC 更新未显示错误但不起作用？

Question

我使用 Netbeans 和 SQLite 作为我的 DBMS。奇怪的是，我可以向数据库添加一条记录，删除一条记录，并显示所有记录，但是，当我尝试更新一条记录时，什么也没有发生，甚至没有错误。有谁知道出什么问题了吗？

import java.sql.*;
import java.util.Scanner;

public class Example
{
    public static void main(String[] args)
    {
        try
        {
            Class.forName( "org.sqlite.JDBC" );
        } catch ( Exception e )
        {
            System.out.println( e );
        }
        Connection c = null;
        try
        {
            c = DriverManager.getConnection( "jdbc:sqlite:Example.db" );
        }
        catch ( SQLException s )
        {
            System.out.println( s );
        }
        String sql = "INSERT INTO Classmates VALUES (?,?,?,?,?)";
        String deleteSQL = "DELETE FROM Classmates WHERE cid = ?";
        String updateSQL = "UPDATE Classmates SET firstname=?,lastname=?,age=?,gpa=? WHERE cid =?";
        String showSQL = "SELECT * FROM Classmates";

        int cid;
        String firstname;
        String lastname;
        double age;
        double gpa;

        char selection;
        boolean valid

        Scanner in = new Scanner( System.in );
        PreparedStatement p = null;
        ResultSet r = null;
        do
        {
            System.out.print("A -Add Classmate\n");
            System.out.print("R - Remove Classmate\n");
            System.out.print("S - Show all Classmates\n");
            System.out.print("U - Update a Classmate\n");
            System.out.print("Q - Quit\n");

            selection = in.next().charAt(0);

            switch(selection)
            {
                case 'a':
                case 'A':
                case 'r':
                case 'R':
                case 's':
                case 'S':
                case 'u':
                case 'U':
                case 'q':
                case 'Q':   valid = true;
                    break;
                default:    valid = false;
            }
            switch(selection)
            {
                case 'a':
                case 'A':
                    System.out.print("Enter cid: ");
                    cid = in.nextInt();
                    in.skip("\n");
                    System.out.print("Enter first name: ");
                    firstname = in.nextLine();
                    System.out.print("Enter last name: ");
                    lastname = in.nextLine();
                    System.out.print("Enter age: ");
                    age = in.nextDouble();
                    System.out.print("Enter the gpa: ");
                    gpa = in.nextDouble();

                    try
                    {
                        p = c.prepareStatement( sql );
                        p.clearParameters();
                        p.setInt( 1, cid );
                        p.setString( 2, firstname );
                        p.setString(3, lastname);
                        p.setDouble(4, age);
                        p.setDouble(5, gpa);
                        p.executeUpdate();
                    }
                    catch ( SQLException s )
                    {
                        System.out.println( s );
                    }
                    break;
                case 'r':
                case 'R':
                    System.out.print("Enter cid: ");
                    cid = in.nextInt();
                    try
                    {
                        p = c.prepareStatement( deleteSQL );
                        p.setInt( 1, sid );

                        // execute SQL delete 
                        p.executeUpdate();
                    }
                    catch ( SQLException s )
                    {
                        System.out.println( s );
                    }
                    break;

                case 's':
                case 'S':
                    try
                    {
                        p = c.prepareStatement( showSQL );
                        p.clearParameters();
                        r = p.executeQuery();

                        while( r.next() )
                        {
                            System.out.println( "CID: " + r.getInt( 1 ) + ", First Name: "
                                + r.getString( 2 ) + ", Last Name: " + r.getString( 3 )
                                + ", Age: " + r.getDouble( 4) + ", GPA: " + r.getDouble(5) );
                        }
                    }
                    catch ( SQLException s )
                    {
                        System.out.println( "Exception 4: " + s );
                    }
                    break;
                case 'u':
                case 'U':
                    System.out.print("Enter cid: ");
                    cid = in.nextInt();
                    in.skip("\n");
                    System.out.print("Update first name: ");
                    firstname = in.nextLine();
                    System.out.print("Update last name: ");
                    lastname = in.nextLine();
                    System.out.print("Update age of student: ");
                    age = in.nextDouble();
                    System.out.print("Update GPA of student: ");
                    gpa = in.nextDouble();
                    try
                    {
                        p = c.prepareStatement( updateSQL );
                        p.clearParameters();
                        p.setInt( 1, cid );
                        p.setString( 2, firstname );
                        p.setString(3, lastname);
                        p.setDouble(4, age);
                        p.setDouble(5, gpa);
                        p.executeUpdate();
                    }
                    catch ( SQLException e )
                    {
                        System.out.println( e.getMessage() );
                    }
                    break;
                case 'q':
                case 'Q':
                    try
                    {
                        r.close();
                        c.close();
                    }
                    catch( SQLException s )
                    {
                        System.out.println( "Exception 5: " + s );
                    }
                    break;
                default:
                    System.out.println("Wrong Selection");
            }
        }while (selection != 'q' || selection != 'Q');
    }
}

Answer 1

您的更新代码有 p.setInt( 1, cid ); 但 cid 字段列在语句的最后: String updateSQL = "UPDATE Classmates SET fname=?,lname= ?,age=?,gpa=?WHERE sid =?";