mysql_fetch_row和mysql_fetch_array之间的冲突

I have a function in PHP that give me some values from DB

$select = mysql_query("SELECT * FROM sfide WHERE accepted = 0");

if($select){
    if(mysql_fetch_row($select) != 0){
        $sep = "~";
        $return = "";
        $i = 0;
        while($row = mysql_fetch_array($select)){
            if($i > 0){
                $return = $return.",";
            };
            $return = $return.$row['id'].$sep.$row['from_'];
            $i += 1;
        }
        return $return;
    }else{
        return "NO";
    }
}else{
return "E, 000, SELECT, ".mysql_error();        
}

The problem is that if I do like in the code above it returns me nothing, instead, if I duplicate the select variable it works:

$select = mysql_query("SELECT * FROM sfide WHERE accepted = 0");
$num_select = mysql_query("SELECT * FROM sfide WHERE accepted = 0");
if($select){
    if(mysql_fetch_row($num_select) != 0){
        $sep = "~";
        $return = "";
        $i = 0;
        while($row = mysql_fetch_array($select)){
            if($i > 0){
                $return = $return.",";
            };
            $return = $return.$row['id'].$sep.$row['from_'];
            $i += 1;
        }
        return $return;
    }else{
        return "NO";
    }
}else{
return "E, 000, SELECT, ".mysql_error();        
}

Why ?