Thanks Eric!
You're absolutely right!

>The UNION operator will not match fields from table. It will only append the result of the second SELECT to the first.

>For example, if you have record A, B and C in the OLD_TABLE and C, D and E in the NEW_TABLE, you will get A, B, C, D, E if you use the UNION (or A, B, C, C, D, E if you use UNION ALL).

>I think that what you need is a JOIN:
SELECT *
FROM Original_table AS O
INNER JOIN New_table AS N
ON N.JoinedField = O.JoinedField

>Notice that you will need a field (JoinedField - normally a primary key) that has the same value in both table to be able to join them.