插入sql server中的sql_variant列

Question

I am trying to insert a value to sql_variant column in sql server from an xml column

ex.

 INSERT INTO 
  [dbo].[TestColumn]
 (
  Id,
  Attribute,
  AttributeValue
 )
 SELECT 
  Id, 
  'TestName', 
  CAST(CustomColumns.query('//TestName') AS nVarchar(MAX))
 FROM 
  [dbo].[Clmnt] (NOLOCK) 

I got this error,

Operand type clash: nvarchar(max) is incompatible with sql_variant

Anybody has any clue on this, How do I easily insert a value in sql_variant?

Answer 1

sql_variant can not store nvarchar(max)

sql_variant (Transact-SQL)

That link says that the following the types of values cannot be stored by using sql_variant:

varchar(max)
varbinary(max)
nvarchar(max)
xml
text
ntext
image
timestamp
sql_variant
geography
hierarchyid
geometry
User-defined types

Answer 2

Sql_variant does support strings. For SQL Server 2008 R2:

nvarchar(4000) but not nvarchar(max).
varchar(8000) but not varchar(max)

The docs I had found were a bit vague on these thresholds.