Create indexed view - sql

Question

My table structure is below :
MyTable (ID Int, AccID1 Int, AccID2 Int, AccID3 int)
ID AccID1 AccID2 AccID3
---- -------- -------- --------
1 12 2 NULL
2 4 12 1
3 NULL NULL 5
4 7 NULL 1
I want to create indexed view with below output :
ID Level Value
---- ----- -------
1 1 12
1 2 2
2 1 4
2 2 12
2 3 1
3 3 5
4 1 7
4 3 1
EDIT :
My table is very huge and I want to have above output.
I can Get my query such as below :
Select ID,
Case StrLevel
When 'AccID1' Then 1
When 'AccID2' Then 2
Else 3
End AS [Level],
AccID as Value
From (
Select A.ID, A.AccID1, A.AccID2, A.AccID3
From MyTable A
)as p
UNPIVOT (AccID FOR [StrLevel] IN (AccID1, AccID2, AccID3)) AS unpvt
or
Select *
from (
select MyTable.ID,
num.n as [Level],
Case Num.n
When 1 Then MyTable.AccID1
When 2 Then MyTable.AccID2
Else MyTable.AccID3
End AS AccID
from myTable
cross join (select 1
union select 2
union select 3)Num(n)
)Z
Where Z.AccID IS NOT NULL
or
Select A.ID,
2 AS [Level],
A.AccID1 AS AccID
From MyTable A
Where A.AccID1 IS NOT NULL
Union
Select A.ID,
2 AS [Level],
A.AccID2
From MyTable A
Where A.AccID2 IS NOT NULL
Union
Select A.ID,
3 AS [Level],
A.AccID3
From MyTable A
Where A.AccID3 IS NOT NULL
But Above query is slow and I want to have indexed view to have better performance.
and in indexed view I can't use UNION or UNPIVOT or CROSS JOIN in indexed view.

Answer 1

What if you created a Numbers table to essentially do the work of your illegal CROSS JOIN?
Create Table Numbers (number INT NOT NULL PRIMARY KEY)
Go
Insert Numbers
Select top 30000 row_number() over (order by (select 1)) as rn
from sys.all_objects s1 cross join sys.all_objects s2
go
Create view v_unpivot with schemabinding
as
Select MyTable.ID,
n.number as [Level],
Case n.number
When 1 Then MyTable.AccID1
When 2 Then MyTable.AccID2
Else MyTable.AccID3
End AS AccID
From dbo.Mytable
Join dbo.Numbers n on n.number BETWEEN 1 AND 3
go
Create unique clustered index pk_v_unpivot on v_unpivot (ID, [Level])
go
Select
ID,
[Level],
AccID
From v_unpivot with (noexpand)
Where AccID IS NOT NULL
Order by ID, [Level]
The WHERE AccID IS NOT NULL must be part of the query because derived tables are not allowed in indexed views.