How do I retrieve aliased items and/or items in SQL

I have a table of items in SQL Server 2008 which are setup as follows:

ITEMS TABLE

itemId (PK) | Ref 
1           | item1
2           | item2

I also have a table to store aliases of these items:

ALIASES TABLE

aliasId(PK) | objectId(FK) | AliasOfId(FK) | Ref 
10          | 50           | 1             | A1
20          | 51           | 2             | A2
30          | 52           | 2             | A3

I am trying to produce a query to so that I can retrieve a list of items but I'm having problem in that I can only seem to get either items OR aliases not both (problem I'm having is LEFT JOIN always joins to aliases.

SQL used is below. Any ideas, appreciate any help?

SELECT  
      ISNULL(A.objectId,I.itemId) AS itemId 
     ,ISNULL(A.ref,I.ref) AS ref
     ,isAlias = CASE WHEN A.aliasID IS NULL 开发者_JAVA百科THEN 1 ELSE 0 END

FROM        items I
LEFT JOIN   aliases A ON (I.itemId = A.AliasOfId)
WHERE       
      ISNULL(A.objectId,I.itemId) = 1
   OR ISNULL(A.objectId,I.itemId) = 51
   OR ISNULL(A.ref,I.ref) = 'A3'

I had put data in with the question but it seems to have reformatted it. Here's the full data in SQL 2008.

CREATE TABLE [items]
( [itemId] [int] NOT NULL
, [ref] [varchar](50) NOT NULL )
 ON [PRIMARY]

CREATE TABLE [aliases]
( [aliasId] [int] NOT NULL
, [objectId] [int] NOT NULL
, [aliasOfId] [int] NOT NULL
, [ref] [varchar](50) NOT NULL )
 ON [PRIMARY]

 INSERT INTO [items] ([itemId],[ref])
 VALUES (1, 'Item1'),(2, 'Item2')

 INSERT INTO [aliases] ([aliasId],[objectId],[aliasOfId],[ref])
 VALUES
 (10, 50, 1, 'A1')
,(20, 51, 2, 'A2')
,(30, 52, 2, 'A3')

    SELECT  
        Ref          AS item
        ItemId 
        Ref
        1            AS isAlias
    FROM 
        items i
UNION ALL
    SELECT  
        i.Ref        AS item
        a.objectID   AS itemId 
        a.Ref        AS ref
        0            AS isAlias
    FROM 
        items i
      JOIN
        aliases a
          ON i.itemId = a.AliasOfId