How to export My Sql Database Backup in php?

$backuptime = "DB_Backup_".DB_NAME."-".time().".sql";
//$backuptime = DB_NAME.".sql";
$data["db_file_name"] = $backuptime;
$insert = $CommonObj->insert_query("db_backup",$data);
$str = "";
$show_tables = "show tables from ".DB_NAME;
$tables = $db->query($show_tables);
if($tables){
   while($row = mysql_fetch_assoc($tables)){
      $table = $row["Tables_in_".DB_NAME];
      $show_each_tables = "show create table ".$table;
      $each_tables  =  $db->query($show_each_tables);
      $each_tables = mysql_fetch_assoc($each_tables);
      $str .= $each_tables["Create Table"];
      $str .= ";\n\n";
      $show_column = "SHOW COLUMNS FROM $table";
      $column  =  $db->query($show_column);
      $get_val_query = "select * from $table";
      $get_val  =  $db->query($get_val_query);
      if($column && mysql_num_rows($get_val)>0){
         $str .= "INSERT INTO `$table` (";
         while($cols = mysql_fetch_assoc($column)){
            $str .= '`'.$cols["Field"].'`, ';
         }
         $str = substr($str,0,-2);
         $str .=  ") VALUES \n";
      }
      if($get_val && mysql_num_rows($get_val)>0){
         while($vals = mysql_fetch_assoc($get_val)){
            $str .= "( ";
            foreach($vals as $k=>$v){
               $v= mysql_real_escape_string($v);
               $str  .= '"'.$v.'", ';
            }
            $str = substr($str,0,-2);
            $str .= "),\n";
         }
         $str = substr($str,0,-2);
      }
      $str .= ";\n\n";
   }
}
$handle = fopen(DIR_DB.$backuptime,'w+');
fwrite($handle,$str);
fclose($handle);