title: Checking if username already exists within the databasae
body: <p>i am trying to check against the database table "user" to see if the "username" exists so that the same username cannot be created again. I want this to be a validator so if the username exists the message box will show it exists.</p>
  
  <p>Please guide me through this, i have the following code so far behind the button to add and check if username exists:</p>
  
  <pre><code>private void btnSignupNew_Click(object sender, EventArgs e)
          {
  
             if (txtUsername.Text == "")
             {
                 errorUsername.SetError(txtUsername, "Enter A Username");
             }
  
             else if (txtPassword.Text == "")
             {
                 errorPassword.SetError(txtPassword, "Enter A Valid Password");
             }
  
                 //so if there isnt no error in the fields itll go on and add the data in to the database.
             else{
  
              //instance of sqlConnection
              SqlConnection con = new SqlConnection("Data Source=etc");
  
              //instance of sqlCommand
              SqlCommand cmd = new SqlCommand("INSERT INTO [User] values ('" + txtForename.Text + "', '" + txtSurname.Text + "', '" + txtUsername.Text + "', '" + txtPassword.Text + "' )", con);
              con.Open();
              cmd.ExecuteNonQuery();
  
              //query executed correcty or not
             con.Close();
  </code></pre>