Row_Number() with union query

Question

I have an sql query that returns rows from two tables with same column names. I need a row number of all records in a complete result set.

Following is the query

select Id, VersionNumber from documents where id=5 
Union all  
select Id, VersionNumber from versions where id=5
order by VersionNumber desc

How should it be done?

EDIT: And what if I only need to return a row_num where VersionNumber is lets say 5.

Answer 1

A slightly better way would be :-

with resultset1 as(
   select Id, VersionNumber from documents where id=5 
   Union all  
   select Id, VersionNumber from versions where id=5
), resultset2 as(
   select Id, VersionNumber, ROW_NUMBER() OVER(ORDER BY Id) ROW_NUM
   from resultset1
)
select * from resultset2 WHERE VersionNumber = 5 

Answer 2

Try this:

SELECT *, ROW_NUMBER() OVER(ORDER BY Id) ROW_NUM
  FROM (
        select Id, VersionNumber from documents where id=5 
        Union all  
        select Id, VersionNumber from versions where id=5
       ) a
order by VersionNumber desc

TO filter by version number 5 use:

SELECT * 
FROM   (SELECT *, 
               Row_number() OVER(ORDER BY versionnumber DESC, id) row_num 
        FROM   (SELECT id, 
                       versionnumber 
                FROM   documents 
                WHERE  id = 5 
                UNION ALL 
                SELECT id, 
                       versionnumber 
                FROM   versions 
                WHERE  id = 5) a) b 
WHERE  version = 5