[FIXED] What do you call the <database>.<table> syntax in SQL?

Issue

In many databases, when writing a SELECT query, you can provide the database name along with the table name in order to resolve any ambiguity the database might encounter in case there are multiple databases with the same table names.

For example, let's say the user currently logged into SQL Server has SELECT privileges on databases DB1 and DB2, and BOTH databases have a table named CUSTOMERS. The following query would return an error stating that the table name is too ambiguous:

SELECT * FROM CUSTOMERS

The solution is to be more specific so the database knows which table to query from:

SELCT * FROM DB1.CUSTOMERS

My question is, what is the name for the <database>.<table> syntax in SQL? I'm asking so that my terminology is correct when explaining it to junior devs.

Solution

These are typically called "qualified" and names, and they can be used when an "unqualified" name is ambiguous, for example when a select query pulls data from multiple tables that share column names.

Answered By - user229044

Answer Checked By - Mary Flores (PHPFixing Volunteer)

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[FIXED] What is a lambda (function)?

Issue

For a person without a comp-sci background, what is a lambda in the world of Computer Science?

Solution

Lambda comes from the Lambda Calculus and refers to anonymous functions in programming.

Why is this cool? It allows you to write quick throw away functions without naming them. It also provides a nice way to write closures. With that power you can do things like this.

Python

def adder(x):
    return lambda y: x + y
add5 = adder(5)
add5(1)
6

As you can see from the snippet of Python, the function adder takes in an argument x, and returns an anonymous function, or lambda, that takes another argument y. That anonymous function allows you to create functions from functions. This is a simple example, but it should convey the power lambdas and closures have.

Examples in other languages

Perl 5

sub adder {
    my ($x) = @_;
    return sub {
        my ($y) = @_;
        $x + $y
    }
}

my $add5 = adder(5);
print &$add5(1) == 6 ? "ok\n" : "not ok\n";

JavaScript

var adder = function (x) {
    return function (y) {
        return x + y;
    };
};
add5 = adder(5);
add5(1) == 6

JavaScript (ES6)

const adder = x => y => x + y;
add5 = adder(5);
add5(1) == 6

Scheme

(define adder
    (lambda (x)
        (lambda (y)
           (+ x y))))
(define add5
    (adder 5))
(add5 1)
6

C# 3.5 or higher

Func<int, Func<int, int>> adder = 
    (int x) => (int y) => x + y; // `int` declarations optional
Func<int, int> add5 = adder(5);
var add6 = adder(6); // Using implicit typing
Debug.Assert(add5(1) == 6);
Debug.Assert(add6(-1) == 5);

// Closure example
int yEnclosed = 1;
Func<int, int> addWithClosure = 
    (x) => x + yEnclosed;
Debug.Assert(addWithClosure(2) == 3);

Swift

func adder(x: Int) -> (Int) -> Int{
   return { y in x + y }
}
let add5 = adder(5)
add5(1)
6

PHP

$a = 1;
$b = 2;

$lambda = fn () => $a + $b;

echo $lambda();

Haskell

(\x y -> x + y) 

Java see this post

// The following is an example of Predicate : 
// a functional interface that takes an argument 
// and returns a boolean primitive type.

Predicate<Integer> pred = x -> x % 2 == 0; // Tests if the parameter is even.
boolean result = pred.test(4); // true

Lua

adder = function(x)
    return function(y)
        return x + y
    end
end
add5 = adder(5)
add5(1) == 6        -- true

Kotlin

val pred = { x: Int -> x % 2 == 0 }
val result = pred(4) // true

Ruby

Ruby is slightly different in that you cannot call a lambda using the exact same syntax as calling a function, but it still has lambdas.

def adder(x)
  lambda { |y| x + y }
end
add5 = adder(5)
add5[1] == 6

Ruby being Ruby, there is a shorthand for lambdas, so you can define adder this way:

def adder(x)
  -> y { x + y }
end

R

adder <- function(x) {
  function(y) x + y
}
add5 <- adder(5)
add5(1)
#> [1] 6

Answered By - mk.

Answer Checked By - Marilyn (PHPFixing Volunteer)

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[FIXED] Where and how is the term used WRAPPER in programming, what does it help to do?

Issue

I come across software developers using the term of creating Wrappers of other classes or APIs or even some codes, this is a term used by experienced Software Programmers

So any idea what do they mean by it;

e.g. a simple question; we got two types of array sorting techniques, lets create a wrapper for it

The above one is a very simple example

Solution

The term 'wrapper' gets thrown around a lot. Generally its used to describe a class which contains an instance of another class, but which does not directly expose that instance. The wrapper's main purpose is to provide a 'different' way to use wrapped object (perhaps the wrapper provides a simpler interface, or adds some functionality).

The word 'wrapper' can also be used when describing classic design patterns.

Wrapping an object to provide a simplified interface to it is often described as the 'Facade' pattern. The wrapper is the facade.

Sometimes you may have a class which would suit a specific interface, but you can't change the code for it to make it conform to that interface. You can create a wrapper for that class which implements the interface, but which directs most of the calls to the wrapped object. This is the 'Adapter' pattern. The wrapper is the adapter.

The instance you describe, where you have two classes which can do array sorting using different algorithms sounds like the 'Strategy' pattern, where you provide a way to perform an operation on some object, but the algorithm used for that operation may be different depending upon the structure of that object.

For example, one of your sort algorithms may be great for arrays of length less than 100, but then performance might be an issue for it. The other algorithm might be good for bigger arrays. You can create a 'wrapper' for the two algorithms which supports the sort operation but decides which algorithm to use based on the array length.

The vast majority of wrappers exist to hide some sort of complexity.

Answered By - Alex Humphrey

Answer Checked By - Timothy Miller (PHPFixing Admin)

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[FIXED] What is the naming standard for path components?

Issue

I keep getting myself in knots when I am manipulating paths and file names because I don’t follow a naming standard for path components.

Consider the following toy problem (Windows example, but hopefully the answer should be platform independent). You have been given the path of a folder:

C:\users\OddThinking\Documents\My Source\

You want to walk the folders underneath and compile all the .src files to .obj files.

At some point you are looking at the following path:

C:\users\OddThinking\Documents\My Source\Widget\foo.src

How would you name the following path components?

A. foo
B. foo.src
C. src
D. .src
E. C:\users\OddThinking\Documents\My Source\ (i.e. the absolute path of the root)
F. Widget\foo.src (i.e. the relative path of the file)
G. Widget\
H. C:\users\OddThinking\Documents\My Source\Widget\
I. C:\users\OddThinking\Documents\My Source\Widget\foo.src

Here is my attempt:

A. Base name? Basename?

B. File name? Filename? The difference is important when choosing identifier names, and I am never consistent here.

C. Extension?

D. Extension? Wait, that is what I called C. Should I avoid storing the dot, and just put it in when required? What if there is no dot on a particular file?

E. ?

F. ?

G. Folder? But isn’t this a Windows-specific term?

H. Path name? Pathname? Path?

I. File name? Wait, that is what I called C. Path name? Wait, that is what I called H.

Solution

I think your search for a "standard" naming convention will be in vain. Here are my proposals, based on existing, well-known programs:

A) C:\users\OddThinking\Documents\My Source\Widget\foo.src
                                                   ---

Vim calls it file root (:help filename-modifiers)

B) C:\users\OddThinking\Documents\My Source\Widget\foo.src
                                                   -------

file name or base name

C) C:\users\OddThinking\Documents\My Source\Widget\foo.src
                                                       ___ (without dot)

file/name extension

D) C:\users\OddThinking\Documents\My Source\Widget\foo.src
                                                      ____ (with dot)

also file extension. Simply store without the dot, if there is no dot on a file, it has no extension

E) C:\users\OddThinking\Documents\My Source\Widget\foo.src
   -----------------------------------------

top of the tree
No convention, git calls it base directory

F) C:\users\OddThinking\Documents\My Source\Widget\foo.src
                                            --------------

path from top of the tree to the leaf
relative path

G) C:\users\OddThinking\Documents\My Source\Widget\foo.src
                                            ------

one node of the tree
no convention, maybe a simple directory

H) C:\users\OddThinking\Documents\My Source\Widget\foo.src
   ------------------------------------------------

dir name

I) C:\users\OddThinking\Documents\My Source\Widget\foo.src
   -------------------------------------------------------

full/absolute path

Answered By - blinry

Answer Checked By - Dawn Plyler (PHPFixing Volunteer)

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[FIXED] What is JSONP, and why was it created?

Issue

I understand JSON, but not JSONP. Wikipedia's document on JSON is (was) the top search result for JSONP. It says this:

JSONP or "JSON with padding" is a JSON extension wherein a prefix is specified as an input argument of the call itself.

Huh? What call? That doesn't make any sense to me. JSON is a data format. There's no call.

The 2nd search result is from some guy named Remy, who writes this about JSONP:

JSONP is script tag injection, passing the response from the server in to a user specified function.

I can sort of understand that, but it's still not making any sense.

---

So what is JSONP? Why was it created (what problem does it solve)? And why would I use it?

---

Addendum: I've just created a new page for JSONP on Wikipedia; it now has a clear and thorough description of JSONP, based on jvenema's answer.

Solution

It's actually not too complicated...

Say you're on domain example.com, and you want to make a request to domain example.net. To do so, you need to cross domain boundaries, a no-no in most of browserland.

The one item that bypasses this limitation is <script> tags. When you use a script tag, the domain limitation is ignored, but under normal circumstances, you can't really do anything with the results, the script just gets evaluated.

Enter JSONP. When you make your request to a server that is JSONP enabled, you pass a special parameter that tells the server a little bit about your page. That way, the server is able to nicely wrap up its response in a way that your page can handle.

For example, say the server expects a parameter called callback to enable its JSONP capabilities. Then your request would look like:

http://www.example.net/sample.aspx?callback=mycallback

Without JSONP, this might return some basic JavaScript object, like so:

{ foo: 'bar' }

However, with JSONP, when the server receives the "callback" parameter, it wraps up the result a little differently, returning something like this:

mycallback({ foo: 'bar' });

As you can see, it will now invoke the method you specified. So, in your page, you define the callback function:

mycallback = function(data){
  alert(data.foo);
};

And now, when the script is loaded, it'll be evaluated, and your function will be executed. Voila, cross-domain requests!

It's also worth noting the one major issue with JSONP: you lose a lot of control of the request. For example, there is no "nice" way to get proper failure codes back. As a result, you end up using timers to monitor the request, etc, which is always a bit suspect. The proposition for JSONRequest is a great solution to allowing cross domain scripting, maintaining security, and allowing proper control of the request.

These days (2015), CORS is the recommended approach vs. JSONRequest. JSONP is still useful for older browser support, but given the security implications, unless you have no choice CORS is the better choice.

Answered By - Jerod Venema

Answer Checked By - Willingham (PHPFixing Volunteer)

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[FIXED] What is JSONC? Are JSONC and JSON-C different?

Issue

Recently came across the term JSONC in a YouTube API. I browsed the Web, but found nothing much about it. Can someone explain whether these two are the same or different?

Solution

JSON-C seems to just be a variation of JSON mainly targeted at C development. I.e., from the open source docs, "JSON-C implements a reference counting object model that allows you to easily construct JSON objects in C, output them as JSON formatted strings and parse JSON formatted strings back into the C representation of JSON objects."ref^1

From the YouTube API perspective (specifically, version 2, not the new version 3), The JSON-C response is just a condensed version of the JSON response (removing "duplicate, irrelevant or easily calculated values").ref^2

Why would the JSON response have "duplicate, irrelevant or easily calculated values" values anyway? Because it is converting the original ATOM XML format directly to JSON in a loseless conversion. You can find out more details here.

However, I would suggest using version 3 of the YouTube Data API. It is much easier to use. =)

Answered By - codingjeremy

Answer Checked By - Gilberto Lyons (PHPFixing Admin)

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[FIXED] How can this be called Pass By Reference?

Issue

According to this tutorial, Python uses "Pass By Reference."

They then go on to give the following example. On what planet is this "Pass By Reference"? It looks like a clear cut case of "Pass By Value" to me.

Thoughts?

def changeme( mylist ):
   mylist = [1,2,3,4];
   print "Values inside the function: ", mylist
   return

mylist = [10,20,30];
changeme( mylist );
print "Values outside the function: ", mylist

The parameter mylist is local to the function changeme. Changing mylist within the function does not affect mylist. The function accomplishes nothing and finally this would produce the following result:

# Values inside the function:  [1, 2, 3, 4]
# Values outside the function:  [10, 20, 30]

---

Update, Conclusion:

1. per answer by viraptor below, "according to the docs, python is pass-by-value". So the tutorial is clearly wrong.

2. Python is not "call by reference", it is "call by sharing". This means a reference can be passed to a local subroutine, updated by the subroutine, and the update stays local to the subroutine and doesn't automatically affect the global value of the reference.

Solution

It is neither. It is call by sharing. I've also heard the term "pass by reference value" used.

Also known as "call by object" or "call by object-sharing," call by sharing is an evaluation strategy first named by Barbara Liskov et al. for the language CLU in 1974. It is used by languages such as Python, Iota, Java (for object references), Ruby, JavaScript, Scheme, OCaml, AppleScript, and many others. However, the term "call by sharing" is not in common use; the terminology is inconsistent across different sources. For example, in the Java community, they say that Java is call-by-value, whereas in the Ruby community, they say that Ruby is call-by-reference, even though the two languages exhibit the same semantics. Call by sharing implies that values in the language are based on objects rather than primitive types, i.e. that all values are "boxed".

The semantics of call by sharing differ from call by reference in that assignments to function arguments within the function aren't visible to the caller (unlike by reference semantics), so e.g. if a variable was passed, it is not possible to simulate an assignment on that variable in the caller's scope. However, since the function has access to the same object as the caller (no copy is made), mutations to those objects, if the objects are mutable, within the function are visible to the caller, which may appear to differ from call by value semantics. Mutations of a mutable object within the function are visible to the caller because the object is not copied or cloned — it is shared.

Answered By - Amadan

Answer Checked By - Dawn Plyler (PHPFixing Volunteer)

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[FIXED] What does '# noqa' mean in Python comments?

Issue

While searching through a Python project, I found a few lines commented with # noqa.

import sys
sys.path.append(r'C:\dev')
import some_module   # noqa

What does noqa mean in Python? Is it specific to Python only?

Solution

Adding # noqa to a line indicates that the linter (a program that automatically checks code quality) should not check this line. Any warnings that code may have generated will be ignored.

That line may have something that "looks bad" to the linter, but the developer understands and intends it to be there for some reason.

For more information, see the Flake8 documentation for Selecting and Ignoring Violations.

Answered By - jimf

Answer Checked By - Mary Flores (PHPFixing Volunteer)

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[FIXED] What is the difference between reverse proxy and web server?

Issue

I read an awesome post on application server vs. webserver at What is the difference between application server and web server?. Moreover, Difference between proxy server and reverse proxy server nicely explains what a proxy server is.

I also learned that some web servers, such as Apache, have reverse proxy built-in. (Source). Also, Wikipedia (https://en.wikipedia.org/wiki/Reverse_proxy) has an image that shows webserver and reverse proxy as separate entities.

Source: https://en.wikipedia.org/wiki/Reverse_proxy (image originally via Privacy Canada, now CC0, license info)

So, I am not sure about the difference between webserver and reverse proxy. Can someone please shed the light?

Solution

A web server listens for HTTP requests and reacts to them by sending back an HTTP response.

A reverse proxy is a web server which determines what response to make by also implementing an HTTP client.

Client A makes an HTTP request to the reverse proxy. The reverse proxy makes an HTTP request to Server B. Server B sends an HTTP response to the reverse proxy. The reverse proxy sends that data as its HTTP response to client A.

Answered By - Quentin

Answer Checked By - Terry (PHPFixing Volunteer)

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