Question

Here is a pseudo code what I want.
I need to get count of fist union in following statement.

SELECT *  
FROM Table1 
UNION 
SELECT Cats.Id + (SELECT COUNT(*) FROM Fist_Union_Result), 
       Cats.Name 
FROM Table2

Any idea ?

Answer 1

Assuming that the first part is a complex query, you could use the with clause to alias it. That allows you to use it in two places, the top part of the union and the place where you count:

; with  FirstPart as
        (
        select  *
        from    Table1
        )
select  *
from    FirstPart
union all
select  cats.Id - cnt.cnt
,       cats.Name
from    Table2 cats
cross join
        (
        select  count(*) as cnt
        from    FistPart
        ) as cnt

If you just want a unique ID, you could place the union in a subquery and just label the rows 1..N:

select  row_number() over (order by Name) as Id
,       Name
from    (
        select  Name
        from    Table1
        union all
        select  Name
        from    Table2
        ) as SubQueryAlias