存储过程删除查询

我有存储过程:

ALTER PROCEDURE [dbo].[k_ShoppingCart_DELETE]

@cartGUID nvarchar

AS

DELETE FROM
  [dbo].[k_ShoppingCart]
WHERE
  CartGUID = @cartGUID

当我执行这个时,

exec dbo.k_ShoppingCart_DELETE '32390b5b-a35a-4e32-8393-67d5629192f0'

结果:0行受影响.

但是,当我尝试这个查询时:

Delete FROM k_ShoppingCart Where CartGUID = '32390b5b-a35a-4e32-8393-67d5629192f0'

结果:2行受影响.

这有什么问题？