>If nType = 1 then CCN can have duplicate entries but if nType = 2 then it cannot.

define a computed field and a unique index for it:
combine_check_fields with CASE WHEN conditionUnique THEN constant ELSE PrimaryKey END

A trace:

CREATE TABLE [dbo].[testTable] (
	[id] [int] IDENTITY (1, 1) NOT NULL ,
	[nType] [tinyint] NOT NULL ,
	[cnn] [char] (1) COLLATE Latin1_General_BIN NOT NULL ,
	[checkunique] AS ([cnn] + case when ([nType] = 2) then (space(10)) else (convert(char(10),[id])) end) 
) ON [PRIMARY]
GO

ALTER TABLE [dbo].[testTable] ADD 
	CONSTRAINT [IX_testTable] UNIQUE  NONCLUSTERED 
	(
		[checkunique]
	)  ON [PRIMARY]+
GO

Fabio