select UNION except one column

Question

i have a question:

I want to join two SQL querys into one query using UNION to avoid duplicates, but i need to know if the data comes from the fisrt select query or from the second select query.

Sample data:

 A TABLE                                                B TABLE
-----------------------------------------------------------------------------
01 JOHN                                                01 JOHN
02 JUAN                                                02 PETER
03 MARTIN                                              03 MARTIN

I have something like this:

Select A.code,A.name from A where some conditions
unión
Select B.code,B.name from B where diferent conditions

RESULT TABLE

---

    01 JOHN                                                
    02 JUAN  
    02 PETER
    03 MARTIN

This Works fine, but now if i want to know if the data comes from first query or from the second i think something like this:

Select A.code,A.name, 'A'   from A where some conditions
unión
Select B.code,B.name, 'B'   from B where diferent conditions

RESULT TABLE

---

    01 JOHN  'A'                                              
    01 JOHN  'B'
    02 JUAN  'A'
    02 PETER 'B'
    03 MARTIN 'A'
    03 MARTIN 'B'

But don't avoid "duplicates" because 'A' is diferent to 'B', so the question is, can i do something so that they don't compare the 'A' with the 'B'?, is another way to obtain the expected result?

EDIT:

The expected result

---

    01 JOHN  'A'                                              
    02 JUAN  'A'
    02 PETER 'B'
    03 MARTIN 'A'

Answer 1

Here's another way of doing it:

SELECT code, name, MIN(SourceTable) AS SourceTable
FROM (
  SELECT code, name, 'A' AS SourceTable         
  FROM A

  UNION 

  SELECT code, name, 'B' AS SourceTable         
  FROM B) t
GROUP BY code, name 
ORDER BY code

Demo here

or perhaps:

SELECT code, name, SourceTable
FROM (
  SELECT code, name, SourceTable,
         ROW_NUMBER() OVER (PARTITION BY code, name 
                            ORDER BY SourceTable) AS rn
  FROM (
    SELECT code, name, 'A' AS SourceTable         
    FROM A

    UNION ALL

    SELECT code, name, 'B' AS SourceTable         
    FROM B) t) AS x
WHERE x.rn = 1  

Demo here