SQL Server XQuery: Sequence Expression - What is @x in the code statement of DECLARE @x xml; ? What is N in the code statement of SET @x = N ' '; ?

Question

Hi all,
I did the basic stuff of T-SQL long time ago. I dive in to do the SQL Server XQuery programming. I saw the following set of code statements from a tutotial website:
DECLARE @x xml;
SET @x = N'';
SELECT @x.query('(1,2,(10,11,12,13,14,15)),-6');
1) What is @x in the code statement of DECLARE @x xml;? What is N in the code statement of SET @x = N ' '? 
2) Is the N in the code statement of SET @x = N ' '; absobutally necessary in the SQL Server XQuery programming?  From XQuery Language Reference of SQL Server 2012 Books Online, I saw the following set of code statements:
DECLARE @x XML
SET @x = '<a/>'
SELECT @x.query('if (/a[1]) then "true" else "false"')
go
I wonder why there is no N in the code statement of the XQuery Language Reference?
Please kindly help, clarify my confusions and answer my questions mentioned above.
Thanks in advance,
Scott Chang

Answer 1

@x is a variable with xml data type. An N prefix stands for the string in Unicode. The N is not necessary in the SQL Server XQuery programming if the values of the element or attribute in the xml are not in an international language.
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