Difference in string comparisons between varchar and nvarchar

Question

These statements were executed on SQL Server 2008 R2 Enterprise.  Collation is the default SQL_Latin1_General_CP1_CI_AS.
Any ideas why the difference in behavior?
DECLARE @StringWithCharZero VARCHAR(100), @StringWithoutCharZero VARCHAR(100);
SELECT @StringWithCharZero = CHAR(0) + 'TEST', @StringWithoutCharZero = 'TEST';
IF @StringWithCharZero = @StringWithoutCharZero
BEGIN
PRINT 'VARCHAR EQUAL';
select ASCII(LEFT(@StringWithCharZero, 1)), ASCII(LEFT(@StringWithoutCharZero, 1));
END
ELSE
BEGIN
PRINT 'VARCHAR NOT EQUAL';
select ASCII(LEFT(@StringWithCharZero, 1)), ASCII(LEFT(@StringWithoutCharZero, 1));
END;
GO
DECLARE @StringWithCharZero NVARCHAR(100), @StringWithoutCharZero NVARCHAR(100);
SELECT @StringWithCharZero = NCHAR(0) + N'TEST', @StringWithoutCharZero = N'TEST';
IF @StringWithCharZero = @StringWithoutCharZero
BEGIN
PRINT 'NVARCHAR EQUAL';
select UNICODE(LEFT(@StringWithCharZero, 1)), UNICODE(LEFT(@StringWithoutCharZero, 1));
END
ELSE
BEGIN
PRINT 'NVARCHAR NOT EQUAL';
select UNICODE(LEFT(@StringWithCharZero, 1)), UNICODE(LEFT(@StringWithoutCharZero, 1));
END;
GO

Answer 1

Hello,
I got the followng result after run the query on SQL Server 2008R2 SP2 Enterprise edition:
SQL Server specific version: Microsoft SQL Server 2008 R2 (SP2) - 10.50.4260.0 (X64)   Jul 11 2012 15:47:13   Copyright (c) Microsoft Corporation  Enterprise Edition (64-bit) on Windows NT 6.1 <X64> (Build 7601: Service Pack
1) (Hypervisor)
Please install the latest Service Pack for SQL Server 2008R2, we can get it from the link below:
How to obtain the latest service pack for SQL Server 2008 R2:
http://support.microsoft.com/kb/2527041
Regards,
Elvis Long
TechNet Community Support