How do i check if companyId exist in datsbase

Please can someone help me to complete this code, it was posted here but the code us not complete for me to use. I want to confirm if companyid exist in database if it does not exist display a message, data not found.. but if data exist do nothing just allow user to continue posting. I just want to use this method to make sure that user inserts correct companyid before submitting other data. This is the code: protected void Button1_Click(object sender, EventArgs e) { using (SqlConnection conn = new SqlConnection(System.Configuration.ConfigurationManager.ConnectionStrings["DefaultCSRConnection"].ConnectionString)) { //Open your connection conn.Open(); //Your Select Query //Change this as per your design and provide the TableName and Columname here string selectString = "SELECT COUNT(*) FROM YourTableName WHERE UserName = @UserName"; //Create Command object SqlCommand myCommand = n ...