T-SQL joins

What's the difference between an inner and full join in T-SQL? Or a right versus left join? I never have this at the top of my head when I need it, so for future references I've assembled a little example that shows the resulting difference between them.
Given the following t-sql:

declare @t1 table (id int)
declare @t2 table (id int)
 
insert into @t1 values(1),(2),(3)
insert into @t2 values(3),(4)
 
select 't1' as 'Table name', * from @t1
select 't2' as 'Table name', * from @t2
 
select 'inner join' as 'Join', t1.id as 'Left', t2.id as 'Right'
from @t1 as t1 inner join @t2 as t2 on t1.id = t2.id
 
select 'left join' as 'Join', t1.id as 'Left', t2.id as 'Right'
from @t1 as t1 left join @t2 as t2 on t1.id = t2.id
 
select 'right join' as 'Join', t1.id as 'Left', t2.id as 'Right'
from @t1 as t1 right join @t2 as t2 on t1.id = t2.id
 
select 'full join' as 'Join', t1.id as 'Left', t2.id as 'Right'
from @t1 as t1 full join @t2 as t2 on t1.id = t2.id

This is the result from the joins:

My favorite Windows 7 Hotkeys

I’ve been using Win7 since beta 2 and I like it a lot. It’s in my opinion by far the best Windows operating system – a lot better than both Vista and XP. Not that it’s such an enormous change from Vista. It’s just the sum of all the small things. Like the perceived overall UI performance. The improved task bar. The speed of the start menu. The search on the start menu (I just can’t remember the last time I actually needed to click my way through the start menu to start a program. I just type in whatever app or feature I need to start or open, and 99 out of 100 it comes up among the top 3-4 items). And not at least; the hotkeys:

• Win + Arrow: Docks the active window to the left or right, or minimizes (down arrow) or maximizes (up arrow) it. Or if the window is maximized and you hit Win + Down Arrow, the window will be restored. If you hit the same Win + Down Arrow again it will be minimized.
• Win + Shift + Left/Right Arrow: Moves a window to the monitor on the left or right keeping the same position as it had on the monitor you moved it from.
• Win + Home: Hides all open windows except the active (you can do the same by grabbing hold of the window title bar with the left mouse button (just as if you’d want to move the window around) and ‘shake’ the window you want to leave open)
• Win + T: Puts focus on the taskbar so that you can use the arrow keys to move between the programs on the task bar and then Enter to activate them, Shift+Enter to open a new instance, or the ‘right menu button’ to get up the menu for each program.
• Win + Number: Opens the program on the given index on your taskbar. For instance if you have pinned Outlook to the first position on the task bar, Win + 1 will start Outlook (or maximize it and bring it to the front if it’s minimized or behind some other windows).
• Win + P: Opens up the “Connect to a projector/external display” dialog with the options to show your desktop on the computer only, duplicate it, extend it or show it on the projector (external display) only.
• Win + X: Opens up the “Windows Mobility Center” where you can adjust display brightness, volume, battery mode, wireless connectivity, external display, sync connected devices, and presentation settings.
• Win + Space: Peek at the desktop – that is; make all windows transparent so that you can see the desktop.
• Win + E: Opens the Windows Explorer
• Ctrl + Shift + Esc: Opens the Task Manager
• Win + R: Opens the Run dialog
• Ctrl + Shift (when launching apps): Runs the program as administrator. For instance; open the Run dialog and type ‘cmd.exe’ (or just ‘cmd’). If you just hit Enter you will open the command prompt under the privileges of the user you’re currently logged in as. But if you instead hit Shift+Enter, you will open the command prompt with Administrator privileges.

Some of these are not really new to Win7, but I just threw them in there anyway because they’re just so incredibly useful :)

These hotkeys (or shortcut keys) just makes my working day a little better and a little bit more productive. Mix these in with some of the new features of the Windows Explorer and it can just make your day a bit brighter;

• Shift + Right-click on a folder gives you some extra options compared to just right-click. For instance the “Open command window here” and “Open in new process”.
• Ctrl + Shift + N: Creates a new folder
• Right-click + Drag folder to the Windows Explorer icon on the taskbar pins the folder, so that you can right-click on the Windows Explorer icon on the taskbar and get direct access to the folder from the jump list.

Custom iTunes installation

I love my iPod and I use it almost every day. Mostly I'm listening to podcasts, but also music off course. But I hate iTunes. Or maybe that's a bit strong. I hate the iTunes installer. I think it’s all too intrusive and it doesn't give me all the choices I feel that it should.

If you go to the download page on iTunes’ web site and download the iTunes 8 version suited for your operating system, you’ll get an iTunesSetup.exe file. If you’ve tried to run this file, you might have noticed that you also end up with a bunch of apps and services that you didn’t asked for. This includes;

Bonjour – Apple’s take on implementing the Zeroconf for discovery of services on a local network. The only reason why I might need the Bonjour service, is if I want to share my iTunes library on my LAN. But for now, running iTunes on a single machine, there’s no reason to have this service running around wasting resources.

Apple Mobile Device Support and Mobile Me – Both of these are meant for synchronization between a computer and an iPhone/IPod Touch. I only have an iPod Nano, so why would I need a service to sync between my pc and something I don’t have?

Apple Software Update – This service will check for new updates on regular intervals, just like Windows Update. Luckily it won’t install anything automatically, it will only notify you if there’s a new iTunes version and let you decide if you want to download and install.

QuickTime – I’m not even going to start elaborating why I dislike QuickTime so much. It would just make me angry. Luckily, there are alternatives.

The last one in the package is off course iTunes itself.

As you might have guess by now, there are only one or two out of six that I actually want to have running on my pc. And it’s really not that hard to actually get it that way. It turns out that the iTunesSetup.exe is just a self-extracting package that contains installers for all of the apps and services above. So if you’d like to have a custom install of iTunes without the nagging apps and services that comes out of this black box, you’ll need a packaging-app like WinRAR or 7-Zip. Then you can just extract the iTunesSetup.exe and delete the parts you don’t need/like. The only thing to be aware of is that iTunes requieres QuickTime, but if you’ve installed QuickTime Alternative before running the iTunes installer, you’ll be safe and sound. So to make a short-list of how to install iTunes only and keep your system a bit less cluttered;

1. Download and install QuickTime Alternative
2. Download, but don’t install iTunes
3. Extract ‘iTunesSetup.exe’
4. Delete the files you want need. For me that means everything except iTunes.msi and AppleSoftwareUpdate.msi.
5. Open the command prompt, navigate to the folder where you extracted iTunes.msi, and run the following command; msiexec /i iTunes.msi /passive
6. If you’d like to be reminded of new updates (which you definitely should), run the same command for the updater service; msiexec /i AppleSoftwareUpdate.msi /passive

(If you want the regular GUI-based installation, you can just skip the “/passive” parameter (or just double-click the msi-file in Windows Explorer).)

Now, I didn’t figure out all this by myself. Google helped me find this article by Ed Bott and this thread over at the PC Pitstop forum.

MemberAccessException

Exceptions are meant for those exceptional conditions that never should happened during your programs lifetime, but that you cannot guarantee won't happen. As you might expect from this statement, I'm not a big fan of sprinkling the code with unnecessary exception throws. I find it more useful to test those exceptional cases using unit and integration tests.

Anyway; while studying the source code from the excellent CodeProject article "NHibernate Best Practices with ASP.NET" by Billy McCafferty, I came across this quite interesting use of MemberAccessException;

public IOrderDao OrderDao
{
  get
  {
    if (orderDao == null) {
      throw new MemberAccessException("OrderDao has not yet been initialized");
    }
    return orderDao;
  }
  set { orderDao = value; }
}

If it were me coding this, I’d probably just throw the far more general ApplicationException or something (if I'd throw it all, mind my words in the intro to this post). But I definitely see that the MemberAccessException would be a lot better fit for this exceptional case.

Empty delegate makes event raising easy and thread-safe

I'm currently working on a project that will use some of the guidelines from the WPF Composite Application Guidance. And as I was studying the source code I kept seeing a strange
initialization of events that looked something like this;

public event EventHandler EmptyDelegateEvent = delegate { };

I mean; I do know my way around delegates, but these empty delegates puzzled me. After googling around a bit I found that this was a just a clever way of avoiding null reference exception when raising the event. So instead of this;

public event EventHandler CheckForNullEvent;

void RaiseEvent()
{
  // the usuall way
  if (CheckForNullEvent != null)
    CheckForNullEvent(this, new EventArgs());
}

...you can simply do this;

public event EventHandler EmptyDelegateEvent = delegate { };

void RaiseEvent()
{
   // the easy way
   EmptyDelegateEvent(this, new EventArgs());
}

When using empty delegates you can simply raise the event without checking for null. Note though, that performance wise it will be better to do the "if not null" check than a "delegate {}". But I ran some performance testing to compare the two, and the performance hit is really not that big of an issue. Even though the performance of the empty delegate was 20-30% slower than the null check, the time it takes to do either of them is miniscule. This is really not where you should put your performance tuning effort. A 'null reference exception', which is much more likely to happen if you forget to check for the null, will have a much bigger impact on the overall performance of your application. Or even worse; if a raise condition occurs. Which again reminds me that the correct way of checking the event for null and at the same time making sure it's thread-safe, is this;

void RaiseEvent()
{
   // the thread-safe way
   EventHandler copyOfEvent = CheckForNullEvent;
   if (copyOfEvent != null)
       copyOfEvent(this, new EventArgs());
}

And how many does actually do that? And talking of performance; what about 'developer performance'? Instantiating an empty delegate and no need for null checking or possible raise conditions, means faster coding and less bugs - e.g. better developer performance.