UNION ALL and MINUS result row source identification

Question

Currently I'm perforing multiple MINUS and UNION ALL operations, but after that I would like to identify from which source table row given result row comes. For example:

SELECT * FROM
  (SELECT 1 AS SRC, tab_1.* FROM tab_1
    MINUS
  SELECT 1 AS SRC, tab_2.* FROM tab_2)
  UNION ALL
  (SELECT 2 AS SRC, tab_2.* FROM tab_2
    MINUS
  SELECT 2 AS SRC, tab_1.* FROM tab_1)

Now I have rows that are present in one of above tables and want to know which row exactly I am looking at. Any keys from tables tab_1 and tab_2 are removed, because they make the comparison impossible (they are generated from different sequences), also no business key exists. In that case I need to have something like another artificial key or even ROWID, but how to use ROWID in the above query?

Answer 1

You seem to want things that are only in one table, but not both. It requires a bit more comparison work, but you can just use not exists:

select 1 as src, t1.*
from tab_1 t1
where not exists (select 1 from tab_2 t2 where t2.col1 = t1.col1 and . . . )
union all
select 2 as src, t2.*
from tab_2 t2
where not exists (select 1 from tab_1 t1 where t1.col1 = t2.col1 and . . .);

In this case, the * really does mean all the columns, including key columns. This version assumes the two tables have the same columns in the same order; in practice, you would normally want an explicit column list.

The where clause looks for the values that you want to test for duplication, so these would not include key columns.