Do you know OUTPUT clause?


Today, I'll write about using OUTPUT clause together with INSERT statements. It seems to be that it is not a very well known syntax. However, it is especially useful when use Identity columns to generate keys. Let's start with a simple table:
 Id int Identity (1,1) PRIMARY KEY,
 Code varchar(10),
 UpperCode AS Upper(Code)
The old fashioned approach to retrieve a value of Identity column for a new row is to use SCOPE_IDENTITY(). For example:
INSERT INTO dbo.Main (Code) VALUES ('aaa');
With OUTPUT clause it will look in the following way:
DECLARE @InsertedIdentity TABLE(Id int);
INSERT INTO dbo.Main (Code) OUTPUT INSERTED.Id INTO @InsertedIdentity VALUES ('aaa')
SELECT TOP(1) * FROM @InsertedIdentity
You can say wait a minute. If I want to use OUTPUT I have to declare a table variable first and then use SELECT. It is more complex than just using SCOPE_IDENTITY().

Well, the first benefit is that with OUTPUT clause we can read values from many columns, including these that are computed (as it was shown above). However, the real power of OUTPUT clause can be observed if we want to insert many rows into a table:
DECLARE @ToBeInserted TABLE(Code varchar(10), Name varchar(100));

VALUES ('aaa','1111111111'), ('ddd','2222222222'), ('ccc','3333333333');

DECLARE @Inserted TABLE(Id int, Code varchar(10), UpperCode varchar(10));

INSERT INTO dbo.Main (Code)
FROM @ToBeInserted;

SELECT * FROM @Inserted;
Without OUTPUT we would have to write a nasty loop!

Here is one more example. Let's assume that we have an additional table that references dbo.Main.
 MainId int,
 Name varchar(100),
We want to insert a few rows into dbo.Main and then related rows to dbo.Child. It is quite easy if we use OUTPUT clause.
INSERT INTO dbo.Child (MainId, Name)
SELECT i.Id, tbi.Name
FROM @ToBeInserted tbi
 JOIN @Inserted i ON i.Code = tbi.Code;
Extremely useful thing that you must know!

At the end it is worth mentioning that OUTPUT clause can be also used together with UPDATE, DELETE or MERGE statements.


Oracle VM VirtualBox and Windows 8.1


In my day to day work I use a 64 bit version of Windows 8.1 Pro N. I needed a virtualization software so I decided to use a free Oracle VM Virtual Box. Everything was ok up to the moment when I wanted to install a x64 version of an operating system on a fresh virtual machine. To my surprise VirtualBox reported the following error:

VT-x/AMD-V hardware acceleration has been enabled, but is not operational. Your 64-bit guest will fail to detect a 64-bit CPU and will not be able to boot.

Please ensure that you have enabled VT-x/AMD-V properly in the BIOS of your host computer.

After some time I noticed that VirtualBox stopped showing 64 bit versions in the Version list. Well, it was actually good because I couldn't use a64 bit virtual machines anyway ;) But, I still didn't know why it happened.

I checked BIOS settings and it seemed ok. I searched Internet for the answer but everyone were recommended to verify BIOS configuration what I've already done. I needed a new VM quickly so at that point I installed a x86 version of Windows.

A few days later my colleague Przemek suggested that the problem may be in the conflict between Hyper-V and VirtualBox and that I should disable Hyper-V. It was strange because I've never installed Hyper-V. However, I checked and I discovered that Hyper-V features were enabled on my computer. It seems to me that they are installed by default with the operating system.

The solution was easy. I pressed Win+S and typed Turn windows feature on or off. Then, I cleared a box next to Hyper-V and restarted computer. After that I was able to install a x64 version of a operating system on a virtual machine.

To sum up, if:
  • Your host system is a x64 version of Windows 8.1.
  • Virtualization is enabled in BIOS.
  • You use VirtualBox.
And you cannot install x64 operating system on a virtual machine then try to disable Hyper-V.