function Delete($mysqli,$table_name, $where_clause=''){   

  $whereSQL = '';

  if(!empty($where_clause)) {

    // check to see if the 'where' keyword exists

    if(substr(strtoupper(trim($where_clause)), 0, 5) != 'WHERE') {

      // not found, add keyword

      $whereSQL = " WHERE ".$where_clause;

    } else {

      $whereSQL = " ".trim($where_clause);

    }

  }

  $sql = "DELETE FROM `".$table_name."` ".$whereSQL;

  return mysqli_query($mysqli,$sql);

}