Understanding COMPATIBILITY_LEVEL in SQL Server

Question

I understood that setting a database to a COMPATIBILITY_LEVEL prior to your native one prevented features from being used. However this doesn't seem to be the case. Witness the following SQL script:

CREATE DATABASE Foo
GO
USE Foo
GO
ALTER DATABASE Foo SET COMPATIBILITY_LEVEL = 80
GO

CREATE TABLE Bar
(
    Id UNIQUEIDENTIFIER NOT NULL,
    TestNvcMax NVARCHAR (MAX) NOT NULL, -- Arrived in SQL 2005
    TestDateTime2 DATETIME2 (7) NOT NULL -- Arrived in SQL 2008
)
GO

But this table creates perfectly - any ideas? I would have thought some kind of an error message or warning would have been appropriate

Answer 1

BOL says:

Compatibility level provides only partial backward compatibility with earlier versions of SQL Server.

Also:

New functionality might work under older compatibility levels, but SET options might require adjustments.

I believe that is your case.

Answer 2

Here you can read about the differences between compatibility level 80, 90 and 100. ALTER DATABASE Compatibility Level

Apparently new data types is not affected. I think that compatibility level is there to make SQL Server "behave" like the older version, not prevent you from doing new fancy stuff.