Question

我使用用户登录，管理员登录等在考试系统上工作。当我检查是否输入了用户名时（例如）如果它已经在数据库中，则不返回并再次创建！

try{
  //  Class.forName("com.mysql.jdbc.Driver");
    Connection con = (Connection) DriverManager.getConnection("jdbc:mysql://localhost:3306/big_project_3","root","");
    //imporrrrrrrrrrrrrrrrrrrrrrrtant
    String selectquery = "select count(*)from uesrs where username='" + username + "'and password='" + password + "'";
    Statement stat=con.createStatement();
    System.out.println(selectquery);
    ResultSet rs=stat.executeQuery(selectquery);
    System.out.println(rs.next());
    if(rs.next()==true){
        infoMessage("Already registered ","Welcom");
    }
    else{
        String insertQuery = "insert into uesrs values(null,'" + username_new_student.getText() + "','" + password_new_student.getText() + "','" + First_name_new_student.getText()+"')";

        stat.executeUpdate(insertQuery);
        infoMessage("info is inserted ","Alert!!!!!");
        dispose();
        user_login ul=new user_login();
        ul.setLocationRelativeTo(null);
        ul.setVisible(true);
    }
}
catch (Exception ex) {
    System.out.println(ex);
}

Answer 1

一旦您在rs.next()内调用System.out.println ()，它将向前移动指针。然后，当您在rs.next()条件内调用if时，将不再显示结果。

try{
  //  Class.forName("com.mysql.jdbc.Driver");
    Connection con = (Connection) DriverManager.getConnection("jdbc:mysql://localhost:3306/big_project_3","root","");
    //imporrrrrrrrrrrrrrrrrrrrrrrtant
    String selectquery="select count(*)from uesrs where username='"+username+"'and password='"+password+"'";
    Statement stat=con.createStatement();
    System.out.println(selectquery);
    ResultSet rs=stat.executeQuery(selectquery);

    if(rs.next() ){
        infoMessage("Already registered ","Welcom");
    }
    else{
        String insertQuery="insert into uesrs values(null,'"+username_new_student.getText()+"','"+password_new_student.getText()+"','"+First_name_new_student.getText()+"')";

     stat.executeUpdate(insertQuery);
     infoMessage("info is inserted ","Alert!!!!!");
    dispose();
    user_login ul=new user_login();
    ul.setLocationRelativeTo(null);
    ul.setVisible(true);


    }

}

catch (Exception ex) {
    System.out.println(ex);
}

if（rs.next（））始终不起作用，转到其他位置

1 个答案: