CREATE UNIQUE NONCLUSTERED INDEX [IX_X] ON [dbo].[X] 
(
[XName] ASC,
[XUsersID] ASC,
[IsFilter] ASC
)

CREATE TABLE dbo.Foo
( FooId		INTEGER		NOT NULL
, FooName	VARCHAR(255) NOT NULL
, FooInd	CHAR(1)		NOT NULL
, CONSTRAINT Foo_P PRIMARY KEY (FooId) 
, CONSTRAINT Foo_C_FooInd CHECK (FooInd IN ('Y','N' ) )
)
go
CREATE VIEW FOO_FooNameUnique WITH SCHEMABINDING 
AS 
SELECT	Foo.FooName
FROM	dbo.Foo
WHERE	Foo.FooInd = 'Y'
WITH CHECK OPTION 
go
CREATE UNIQUE CLUSTERED INDEX FOO_FooNameUnique_X
	ON dbo.FOO_FooNameUnique (FooName)
go

delete from dbo.Foo
INSERT INTO dbo.Foo
	(FooId, FooName, FooInd)
SELECT 1 , 'OK'			, 'Y' union all
SELECT 2 , 'Duplicate'	, 'Y'
	
-- Not a duplicate due to filter
INSERT INTO dbo.Foo
	(FooId, FooName, FooInd)
SELECT  3 , 'Duplicate' , 'N'
-- Not a duplicate due to filter
INSERT INTO dbo.Foo
	(FooId, FooName, FooInd)http://www.sqlservercentral.com/Forums/Skins/Classic/Images/RichTextBoxTable/tbl_bottomleft.gif
SELECT  4 , 'Duplicate' , 'N'

-- This is a duplicate and should cause an error
INSERT INTO dbo.Foo
	(FooId, FooName, FooInd)
SELECT  5 , 'Duplicate'	, 'Y'