SQL Server 2012 Collapse / Unpivot Two Columns Into One?

Question

Actual table has about 6 million rows, num1 and num2 in each row represent numeric boundaries. I need to convert the two-column set into a single column, and applying the to each of the two rows that previously shared a single row. Below is a small sample. I looked at Unpivot examples but nothing seems to fit what I need. Can anyone recommend the right way to go? I realize I will end up with 12 million rows in the end.

Thanks.

declare @orig table ( num1 bigint , num2 bigint , metakey tinyint )
insert into @orig 
select 7216,7471  , 0
union all
select 7472,8239  , 1
union all
select 8240,9263  , 2
union all
select 9264,11311 , 3


declare @dest table ( allnum bigint , metakey tinyint )

    -- Wanted result set:
/*
    select * from @dest
    7216        0
    7471        0
    7472        1
    8239        1
    8240        2
    9263        2
    9264        3
    11311       3
*/

I understand that this works for my table variable sample, but for the really big set it does not smell right:

insert into @dest
select num1 , metakey
from @orig
union all 
select num2 , metakey
from @orig
order by 1

Answer 1

Unpivot seams to do what you want.

select u.allnum,
       u.metakey
from @orig as o
  unpivot (allnum for col in (o.num1, o.num2)) as u

Compared to the union query you already have this should be faster because it will only scan the table once instead of twice.

Answer 2

This can be easily done using cross apply

select allnum,metakey from @orig cross apply (values(num1 ), (num2)) x(allnum)

Answer 3

If you can do a two step process, you could do this:

insert @dest (bigint, metakey)
    select num1, metakey from @orig

insert @dest (bigint, metakey)
    select num2, metakey from @orig

If that's not an option, you could do a similar thing by selecting from a derived table, which would be comprised of a union of the two selects above.