conditional statement in sql error in C# [offTopic]

Question

I am trying to create a login system by using parameterised sql and cross-table query.

This is my code for my login in C#:

private void userloigin() {

    using (MySqlConnection connection = new MySqlConnection("datasource=**;port=***;database=***;username=***;password=***;")) {

        MySqlCommand cmd = new MySqlCommand("SELECT * FROM student, teacher WHERE (student.Username = @userName AND student.Password = @passWord) OR (teacher.username = @teacherUser AND teacher.password = @teacherPass);");
        cmd.CommandType = CommandType.Text;
        cmd.Connection = connection;
        cmd.Parameters.AddWithValue("@userName", textboxUsername.Text);
        cmd.Parameters.AddWithValue("@passWord", texBoxPassword.Text);
        cmd.Parameters.AddWithValue("@teacherUser", textboxUsername.Text);
        cmd.Parameters.AddWithValue("@teacherPass", texBoxPassword.Text);
        connection.Open();
        MySqlDataReader DBReader;
        cmd.Connection = connection;
        DBReader = cmd.ExecuteReader();
        int check = 0;
        while (DBReader.Read()) {
            var teacherLogin = DBReader.GetString("username");
            var teacherPass = DBReader.GetString("password");
            var studentLogin = DBReader.GetString("Username");
            var studentPass = DBReader.GetString("Password");

            if (teacherLogin == textboxUsername.Text && teacherPass == texBoxPassword.Text) {
                MessageBox.Show("Login Successfull!");
                this.Hide();
                Registration ss = new Registration();
                ss.Show();
            } else if (studentLogin == texBoxPassword.Text && studentPass == texBoxPassword.Text) {
                MessageBox.Show(" Login Successfull");

                this.Hide();
                Test ss = new Test();
                ss.Show();
            } else {
                MessageBox.Show("Username or Password Incorrect.  Try Again please");
            }
        }   
    }
}

Since username and password is in BOTH tables 'teacher' and 'student'. The login will allow the student to login BUT not the teacher. Which is understandable. However when I do:

tbl_name.col_name

I get an error saying:

An unhandled exception of type 'System.IndexOutOfRangeException' occurred in MySql.Data

Additional information: Could not find specified column in results: teacher.username

 var teacherLogin = DBReader.GetString("teacher.username");
 var teacherPass = DBReader.GetString("teacher.password");
 var studentLogin = DBReader.GetString("student.Username");
 var studentPass = DBReader.GetString("student.Password");

QUESTION:

How can I amend my code so that if the 'teacher' signs in then take the teacher to the registration form.

Same way, if a student signs in then take the student to the test form?

What am I doing wrong?

     using (MySqlConnection connection = new MySqlConnection("datasource=localhost;port=3306;database=project;username=root;password=Greenford123;"))
        {
            MySqlCommand cmd = new MySqlCommand("SELECT student.studentUsername, student.studentPassword, teacher.teacherUsername, teacher.teacherPassword FROM student, teacher WHERE (student.studentUsername = @userName AND student.studentPassword = @passWord) OR (teacher.teacherUsername = @teacherUser AND teacher.teacherPassword = @teacherPass);");
            cmd.CommandType = CommandType.Text;
            cmd.Connection = connection;
            cmd.Parameters.AddWithValue("@userName", textboxUsername.Text);
            cmd.Parameters.AddWithValue("@passWord", texBoxPassword.Text);
            cmd.Parameters.AddWithValue("@teacherUser", textboxUsername.Text);
            cmd.Parameters.AddWithValue("@teacherPass", texBoxPassword.Text);
            connection.Open();
            MySqlDataReader DBReader;
            cmd.Connection = connection;
            DBReader = cmd.ExecuteReader();

            while (DBReader.Read())
            {
                var teacherLogin = DBReader.GetString("teacherUsername");
                var teacherPass = DBReader.GetString("teacherPassword");
                var studentLogin = DBReader.GetString("studentUsername");
                var studentPass = DBReader.GetString("studentPassword");

                if (teacherLogin == textboxUsername.Text && teacherPass == texBoxPassword.Text)
                {
                    MessageBox.Show("Login Successfull!");

                    this.Hide();
                    Registration ss = new Registration();
                    ss.Show();
                }
                else if (studentLogin == texBoxPassword.Text && studentPass == texBoxPassword.Text)
                {
                    MessageBox.Show(" Login Successfull");

                    this.Hide();
                    Test ss = new Test();
                    ss.Show();
                }
                else
                {
                    MessageBox.Show("Username or Password Incorrect.  Try Again please");
                }

            }

EDIT: its working now BUT it only allows the teacher access to the system. If the student tries to login it will say

wrong username or password. try again please

Answer 1

Error is because of this

else if (studentLogin == texBoxPassword.Text && studentPass == texBoxPassword.Text)

Where studentLogin == texBoxPassword.Text hence the

wrong username or password.

Correct this instead with

else if (studentLogin == textboxUsername.Text && studentPass == texBoxPassword.Text)