这个PHP代码有效吗？

I'm currently working on an iOS app, which communicates with a database on a server (REST API). I've managed to send simple post queries to the server and successfully getting responses, but since a few hours I am stuck with the following php-function (it was not written by myself!). My questions:

1. Is this valid php-Code?

2. Is it possible to POST both JSON-Objects and non-JSON Objects at the same time?

3. How would a valid request query look like? (I am using the Google Chrome App "Postman - REST Client" to test the queries) So what would the parameters look like if a wanted to pass tableid = 1, clientid = 1 and json = {1,2,3,4}?

Thank you very much!

if($_POST['function'] == 'addOrder'){

    $sql = "INSERT INTO orders SET
                orderdate = NOW(),
                tableid = '".$_POST['tableid']."',
                clientid = '".$_POST['clientid']."'";
    $result = mysql_query($sql);
    $oid = mysql_insert_id();

    $orderitems = json_decode($_POST['json'],true);

    reset($orderitems);
    while(list(,$oitem) = each($orderitems)){
        $sql = "INSERT INTO orderitems SET
                        orderid = '".$oid."',
                        foodid = '".$oitem['id']."";    
        $result = mysql_query($sql);
    }
}

You ask:

Is it possible to POST both JSON-Objects and non-JSON Objects at the same time?

How would a valid request query look like? (I am using the Google Chrome App "Postman - REST Client" to test the queries) So what would the parameters look like if a wanted to pass tableid = 1, clientid = 1 and json = {1,2,3,4}?

Yes, you can post both JSON and non-JSON in a single request. The JSON {1,2,3} doesn't make sense, though. If it is a simple array, that would be [1,2,3]:

NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];
[request setHTTPMethod:@"POST"];
NSString *messageBody = @"function=addOrder&tableid=1&clientid=2&json=[1,2,3]";
NSData   *messageData = [messageBody dataUsingEncoding:NSUTF8StringEncoding];
[request setValue:@"application/x-www-form-urlencoded" forHTTPHeaderField:@"Content-Type"];
[request setHTTPBody:messageData];
NSOperationQueue *queue = [[NSOperationQueue alloc] init];
[NSURLConnection sendAsynchronousRequest:request queue:queue completionHandler:^(NSURLResponse *response, NSData *data, NSError *error) {
    if (error)
        NSLog(@"sendAsynchronousRequest error: %@", error);
    if (data) {
        NSString *string = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
        NSLog(@"%@", string);
    }
}];

Note, in your while loop, you refer to $oitem['id'], but I don't understand this id you're referring to. Given that $orderitems is a simple array, each item is referenced by $oitem alone, (no ['id']).

And, as an aside, I generally use the foreach syntax:

foreach ($orderitems as $oitem) {
    // now I can refer to $oitem
}

If your JSON was [{"id":1},{"id":2},{"id":3}], then you'd refer to $oitem['id'], but if it's [1,2,3], you just refer to $oitem.