[RESOLVED] Help with registration form!

Hello! I created a registration and login form but I have a problem . When you created a user , you can create it again with different password .
Here is code of Registration form :

Code:

---

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

using MySql.Data.MySqlClient;

namespace SyrX_Messenger
{
    public partial class Reg : Form
    {
        private MySqlConnection conn;
        private string server;
        private string database;
        private string uid;
        private string password;
                 

        public Reg()
                    {
            server = "localhost";
            database = "syrx";
            uid = "root";
            password = "";

            string connString;
            connString = $"SERVER={server};DATABASE={database};UID={uid};PASSWORD={password}";

            conn = new MySqlConnection(connString);
            InitializeComponent();
        }

        private void Button2_Click(object sender, EventArgs e)
        {
            this.Hide();
            var login = new Login();
            login.Closed += (s, args) => this.Close();
            login.Show();
        }

        private void Button1_Click(object sender, EventArgs e)
        {
            if (TextBox3.Text == "")
            {
                MessageBox.Show("Please approve your password");
            }
            else if (TextBox2.Text != TextBox3.Text)
            {
                MessageBox.Show("Passwords do not match");
            }
            else
            {
                string user = TextBox1.Text;
                string pass = TextBox2.Text;

                if (Register(user, pass))
                {
                    MessageBox.Show($"User {user} successfully created");
                }
                else
                {
                    MessageBox.Show($"User {user} did not created!");
                }
            }
        }
        public bool Register(string user, string pass)
        {
        string query = $"INSERT INTO users (id, username, password) VALUES ('', '{user}', '{pass}');";


            try
            {
                if (OpenConnection())
                {
                    MySqlCommand cmd = new MySqlCommand(query, conn);                   
                    try
                    {                       
                        cmd.ExecuteNonQuery();
                        return true;
                    }
                    catch (Exception ex)
                    {
                        return false;
                    }
                }       
                else
                {
                    conn.Close();
                    return false;
                } 
            }
            catch
            {
                conn.Close();
                return false;
            }
        }
        private bool OpenConnection()
        {
            try
            {
                conn.Open();
                return true;
            }
            catch  (MySqlException ex)
            {
                switch (ex.Number)
                {
                    case 0:
                        MessageBox.Show("Can not connect to server");
                        break;
                    case 1045:
                        MessageBox.Show("Server error");
                        break;
                }
                return false;
            }
        }
    }
}

---

I want to do that when you create a new account first it check if username exists and then create or give an error . How can I make that?

When the button is pressed you currently check that the password confirmation has been entered correctly, then call Register (which simply adds a new user to the database).

As you want to avoid creating duplicate users you need to somehow detect if the new record would create a duplicate, and stop if it would.

An easy way to do that would be to query the database at the start of Register (using something like $"SELECT id FROM users WHERE username = {user}" ), and see if it returns any records... if it does, don't add the new user.

Can you help me with code ? I'm new at this. I don't understand all :(

I solved the problem with another way :P . I set the username as unique in mysql database :D . Thanks for help.