while len(@s)<8
select @s=@s+a
from (
select 'A' as a
union all
select 'B' as a
union all
select 'C' as a
union all
...
select 'N' as a
union all
select 'P' as a
union all
...
select 'Z' as a
union all
select '1' as a
union all
select '2' as a
union all
...
select '9' as a
) as t
order by newid()