Question

I have two intermediate result sets in a create view statement. The result sets are derived from two different join paths and I need to union them. But it doesn’t stop here. Since the ID column needs to be unique, I will then need the rows in result set 2 that contains the same IDs as the first result set to overwrite the same rows in the first result set.

Let me illustrate this here:

Result set 1

ID    Value
------------
1     a
3     a
5     a
6     a
7     a
8     a

Result Set 2

ID    Value
------------
2     b
4     b
5     b
7     b
9     b
10    b

End result set
ID    value
------------
1     a
2     b
3     a
4     b
5     b
6     a
7     b
8     a
9     b
10    b

I am not sure how to approach this. Union/except/intersect will create duplicate ids, so that’s no good.

Answer 1

SELECT COALESCE(set2.ID, set1.ID) AS ID,
       CASE WHEN set2.ID IS NULL THEN set1.Value ELSE set2.Value END AS Value
FROM set1
    FULL JOIN set2
        ON set1.ID = set2.ID