StackOverflow is an amazing site for coding questions. It was created by Joel Spolsky of joelonsoftware.com, Jeff Atwood of codinghorror.com, and some other incredibly smart guys who truly care about user experience. I have been a total fan of SO since it went mainstream and it's now a borderline addiction (you can see my StackOverflow badge on the right sidebar).

The Story

So, one day someone at StackOverflow started a "Hidden features of" post about a famous language (I don't feel like finding out which one was first exactly), and it turned out to be so popular that other posts in the same series started popping up.

Such questions were quickly turned into community wikis, for the purposes of harvesting and organizing information coming from the best developers on the planet and voted by users of the site. There are literally hundreds of answers, sorted by votes.

Hidden Features Of

Programming Languages

Hidden features of ActionScript3 / Flex

Hidden features of ASP.NET

Hidden features of x86 assembly

Hidden features of C

Hidden features of C++

Hidden features of C#

Hidden features of ColdFusion

Hidden features of D

Hidden features of Delphi

Hidden features of Erlang

Hidden features of F#

Hidden features of Flash development, Flash language (AS2/3), and Flash IDE

Hidden features of Java

Hidden features of JavaScript

Hidden features of Haskell

Hidden features of Lisp

Hidden features of Lua

Hidden features of Objective-C

Hidden features of Perl

Hidden features of PHP

Hidden features of Python

Hidden features of R

Hidden features of Ruby

Hidden features of Ruby on Rails

Hidden features of Scala

Hidden features of Silverlight

Hidden features and Dark Corners of STL?

Hidden features of TCL/TK

Hidden features of VB.Net

Hidden features of VBA

Databases

Hidden features of MySQL

Hidden features of Oracle

Hidden features of PL/SQL

Hidden features of PostgreSQL

Hidden features of SQL Server

Mobile

Hidden features of Android development

Other

Hidden features of Bash – also see my bash cheatsheet.

Hidden features of CSS

Hidden features of Django

Hidden features of Eclipse

Hidden features of Emacs

Hidden features of Grails

Hidden features of Greasemonkey

Hidden features of HTML

Hidden features of HTTP

Hidden features of jQuery

Hidden features of mod_rewrite

Hidden features of Qt

Hidden features of RegEx

Hidden features of Spring framework

Hidden features of VHDL

Hidden features of Visual Studio (2005-2008)

Hidden features of Windows.Forms

Hidden features of WPF and XAML

Hidden features of Xpath+Xslt

I will try to maintain this list, adding new languages that join the series as I find them. Now go learn something new!

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Here are my findings:

1. The

   UPDATE swap_test SET x=y, y=x;

   approach doesn't work, as it'll just set both values to y.

   PostgreSQL seems to handle this query differently, as it apparently uses the old values throughout the whole query. [Reference]

2. Here's a method that uses a temporary variable. Thanks to Antony from the comments for the "IS NOT NULL" tweak. Without it, the query works unpredictably. See the table schema at the end of the post. This method doesn't swap the values if one of them is NULL. Use method #3 that doesn't have this limitation.

   UPDATE swap_test SET x=y, y=@temp WHERE (@temp:=x) IS NOT NULL;

   The parentheses around @temp:=x are critical. Omitting them will cause data corruption.

   1 2 3

   mysql> UPDATE swap_test SET x=y, y=@temp WHERE (@temp:=x) IS NOT NULL; Query OK, 3 rows affected Rows matched: 3 Changed: 3 Warnings: 0

3. This method was offered by Dipin in the comments. I think it’s the most elegant and clean solution. It works with both NULL and non-NULL values.

   UPDATE swap_test SET x=(@temp:=x), x = y, y = @temp;

4. Another approach I came up with that seems to work:

   UPDATE swaptest s1, swaptest s2 SET s1.x=s1.y, s1.y=s2.x WHERE s1.id=s2.id;

   1 2 3

   mysql> update swap_test s1, swap_test s2 set s1.x=s1.y, s1.y=s2.x where s1.id=s2.id; Query OK, 3 rows affected Rows matched: 3 Changed: 3 Warnings: 0

Essentially, the 1st table is the one getting updated and the 2nd one is used to pull the old data from.

Test schema used:

1
2
3
4
5
6
7
8
9
10

CREATE TABLE `swap_test` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `x` varchar(255) DEFAULT NULL,
  `y` varchar(255) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB;
 
INSERT INTO `swap_test` VALUES ('1', 'a', '10');
INSERT INTO `swap_test` VALUES ('2', NULL, '20');
INSERT INTO `swap_test` VALUES ('3', 'c', NULL);

Do you have a better approach? If so, please share in the comments.

Some references:

• http://stackoverflow.com/questions/37649/swapping-column-values-in-mysql/ – some discussion on various methods, which eventually prompted me to start this post
• http://www.marcworrell.com/article-3026-en.html – discussion on the 2nd approach, which doesn’t work

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Allow me to introduce LOLCODE – perhaps the most serious and, for some, cryptic, programming language. It is Turing-complete and uses an advanced compiler called Brainfuck (I’m still totally serious, and by the way if you’ve never heard of LOLCATS, then you’re not spending nearly enough time on the Internets. See the funny button that looks like a cross at the top right of your IE? Click it or your desktop will turn into a colorful bouquet of dildos in about 8 seconds).

Let’s look at some examples of LOLCODE, taken from Wikipedia.

HAI
CAN HAS STDIO?
PLZ OPEN FILE "LOLCATS.TXT"?
    AWSUM THX
        VISIBLE FILE
    O NOES
        INVISIBLE "ERROR!"
KTHXBYE

Analysis of this complex code is beyond the scope of this article (the scientific value of which is undeniable) but I can tell you this: once you get comfortable with LOLCODE, you will forget all about C and Python. Occasionally you will still desire to use Perl because, well, Perl’s syntax is very close to LOLCODE’s.

Here’s another AWSUM example that introduces loops:

HAI
CAN HAS STDIO?
IM IN YR LOOP UPPIN YR VAR TIL BOTHSAEM VAR AN 10
    VISIBLE SUM OF VAR AN 1
IM OUTTA YR LOOP
KTHXBYE

The program above displays numbers from 1 through 10.

HAI
CAN HAS STDIO?
I HAS A VAR
IM IN YR LOOP
	UPZ VAR!!1
	VISIBLE VAR
	IZ VAR BIGR THAN 10? GTFO. KTHX
KTHX
KTHXBYE

seems to be another way of writing the same thing.

Heated discussions on the subject of LOLCODE, like the introduction of a NOM NOM NOM operator, are going on every day. I, for one, am proposing renaming the KTHXBYE operator to KTHXBAI.

You can find out more about LOLCODE at the official site: http://lolcode.com.

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Basement hackers and amateur mathematicians are competing to improve the program that Netflix uses to recommend DVDs — and to win $1 million in the process.

"THE “NAPOLEON DYNAMITE” problem is driving Len Bertoni crazy. Bertoni is a 51-year-old “semiretired” computer scientist who lives an hour outside Pittsburgh. In the spring of 2007, his sister-in-law e-mailed him an intriguing bit of news: Netflix, the Web-based DVD-rental company, was holding a contest to try to improve Cinematch, its “recommendation engine.” The prize: $1 million.

Cinematch is the bit of software embedded in the Netflix Web site that analyzes each customer’s movie-viewing habits and recommends other movies that the customer might enjoy. (Did you like the legal thriller “The Firm”? Well, maybe you’d like “Michael Clayton.” Or perhaps “A Few Good Men.”) The Netflix Prize goes to anyone who can make Cinematch’s predictions 10 percent more accurate. One million dollars might sound like an awfully big prize for such a small improvement. But in fact, Netflix’s founders tried for years to improve Cinematch, with only incremental results, and they knew that a 10 percent bump would be a challenge for even the most deft programmer. They also knew that, as Reed Hastings, the chief executive of Netflix, told me recently, “getting to 10 percent would certainly be worth well in excess of $1 million” to the company. The competition was announced in October 2006, and no one has won yet, though 30,000 hackers worldwide are hard at work on the problem. Each day, teams submit their updated solutions to the Netflix Prize Web page, and Netflix instantly calculates how much better than Cinematch they are. (There’s even a live “leader board” ranking the top contestants.)

In March 2007, Bertoni decided he wanted to give it a crack. So…"

read more | digg story

Photo and article copyright of NY Times.

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