How to stop value only returning true when selecting boolean column from database [closed]

I am building a login system that has two different user types. Within the user field their is a boolean column called user_isAdmin. If true, the user is an admin, if false the user is a default user. Currently I have written a code that logs in but currently returns true for every user. Here is the first attempt:

    private void confirmBtn_Click(object sender, EventArgs e)
    {
        Connect database = new Connect();
        String username = usernameField.Text;
        String password = passwordField.Text;

        DataTable table = new DataTable();
        MySqlDataAdapter adapter = new MySqlDataAdapter();
        MySqlCommand command = new MySqlCommand("SELECT * From tbl_user WHERE `username` = @uname and `user_password` = @pwd", database.getConnection());
        command.Parameters.Add("uname", MySqlDbType.VarChar).Value = username;
        command.Parameters.Add("pwd", MySqlDbType.VarChar).Value = password;

        adapter.SelectCommand = command;
        adapter.Fill(table);


        if (!checkInputFields())
        {
            if (username.ToLower().Trim().Equals("") || password.Trim().Equals(""))
            {
                /*Please Enter Username or Password*/
                MessageBox.Show("Please Enter Username or Password!", "", MessageBoxButtons.OKCancel, MessageBoxIcon.Error);
            }
            else if (table.Rows.Count > 0)
            {
                /*Login Success for Admin*/
                if (!checkIfAdmin()) {
                    MessageBox.Show("Admin Login Successful!", "", MessageBoxButtons.OK, MessageBoxIcon.Information);
                    this.Hide();
                    HomeAdmin admin = new HomeAdmin();
                    admin.ShowDialog();
                }
                else
                {
                    /*Login Success for user*/
                    MessageBox.Show("User Login Successful!", "", MessageBoxButtons.OK, MessageBoxIcon.Information);
                    this.Hide();
                    HomePlayer user = new HomePlayer();
                    user.ShowDialog();
                }
            }
            else
            {
                /*Login Error No Username*/
                if (username.Trim().Equals(""))
                {
                    MessageBox.Show("Please Enter Your Username", "", MessageBoxButtons.OKCancel, MessageBoxIcon.Error);
                }
                /*Login Error No password*/
                else if (password.Trim().Equals(""))
                {
                    MessageBox.Show("Please Enter Your Password", "", MessageBoxButtons.OKCancel, MessageBoxIcon.Error);
                }
                else
                {
                    /*Login Error Wrong Username or password*/
                        MessageBox.Show("Username or Password is incorrect", "", MessageBoxButtons.OKCancel, MessageBoxIcon.Error);
                }
            }
        }
        else
        {
            MessageBox.Show("Please Enter all your details", "", MessageBoxButtons.OKCancel, MessageBoxIcon.Error);
        }
    }
    /*Check All Fields Have Inputs*/
    public Boolean checkInputFields()
    {
        String username = usernameField.Text;
        String password = passwordField.Text;
        if (username.ToLower().Trim().Equals("username") || password.ToLower().Trim().Equals("password"))
        {
            return true;
        }
        else
        {
            return false;
        }
    }
    public Boolean checkIfAdmin()
    {
        Connect database = new Connect();
        MySqlCommand command = new MySqlCommand("SELECT user_isAdmin From tbl_user WHERE userID = userID", database.getConnection());
        command.Connection.Open();
        bool isAdmin = (bool)command.ExecuteScalar();

        if (isAdmin)
        {
            return true;

        }
        else
        {
            return false;
        }
       
    }

It reaches this section where it calls checkIfAdmin:

if (!checkIfAdmin()) {
                    MessageBox.Show("Admin Login Successful!", "", MessageBoxButtons.OK, MessageBoxIcon.Information);
                    this.Hide();
                    HomeAdmin admin = new HomeAdmin();
                    admin.ShowDialog();
                }
                else
                {
                    /*Login Success for user*/
                    MessageBox.Show("User Login Successful!", "", MessageBoxButtons.OK, MessageBoxIcon.Information);
                    this.Hide();
                    HomePlayer user = new HomePlayer();
                    user.ShowDialog();
                }

This is checkIfAdmin:

    public Boolean checkIfAdmin()
{
    Connect database = new Connect();
    MySqlCommand command = new MySqlCommand("SELECT user_isAdmin From tbl_user WHERE userID = userID", database.getConnection());
    command.Connection.Open();
    bool isAdmin = (bool)command.ExecuteScalar();

    if (isAdmin)
    {
        return true;
    }
    else
    {
        return false;
    }

}

Currently it only returns true which says that all users are admins, even thought they arent. What I want to know is how I can select the user_isAdmin value based on whether or not they are an admin. If they are an admin, calling the checkIsAdming would run:

                    MessageBox.Show("Admin Login Successful!", "", MessageBoxButtons.OK, MessageBoxIcon.Information);
                this.Hide();
                HomeAdmin admin = new HomeAdmin();
                admin.ShowDialog();

Whereas a user would run:

                    MessageBox.Show("User Login Successful!", "", MessageBoxButtons.OK, MessageBoxIcon.Information);
                this.Hide();
                HomePlayer user = new HomePlayer();
                user.ShowDialog();

Here is my user table if it helps: enter image description here

Answer

When you use SELECT user_isAdmin From tbl_user WHERE userID = userID, as others pointed out, you are not selecting a row for a particular user ID, because you’re not passing the userID as a parameter.

The command you used is equivalent to SELECT user_isAdmin From tbl_user WHERE 1 = 1. When you execute this command, it will return a list of the user_isAdmin values for all the users in your table.

In order to achieve what you want, you need to get the user_isAdmin value for the unique user. This could be done by passing userID as a parameter to your SQL query, just like you did here: SELECT * From tbl_user WHERE username = @uname and user_password = @pwd.

The CheckIfAdmin method should look like this:

public Boolean CheckIfAdmin(Guid userId) // or whatever is the type of userId
{
    Connect database = new Connect();
    MySqlCommand command = new MySqlCommand("SELECT user_isAdmin From tbl_user WHERE userID = @userID", database.getConnection());
    command.Parameters.Add("userID", MySqlDbType.Guid).Value = userId;        
    command.Connection.Open();
    bool isAdmin = (bool)command.ExecuteScalar();

    if (isAdmin)
    {
        return true;
    }
    else
    {
        return false;
    }

}

This will get the userID for the user in question.

Of course, before calling CheckIfAdmin, you have to fetch the userID from the database. If the username is unique (which I recommend), you can use it instead of the userID.