Question

Is there any advanced Oracle SQL methods to solve this kind of situation?

Simplified:
Two queries returns primary_key_value and other_value.
Both queries always return primary_key_value but other_value might be null.

So how I can union those two queries so that it returns always those rows which has other_value, but if both queries are having other_value = null with same primary key, then only one row should be returned.

I know this is so stupid case. But specifications were like this 🙂

Example:
First query:

A  |  B
=======
1  | X
2  | 
3  | 
4  | Z

Second query:

A  |  B
=======
1  | Y
2  | 
3  | Z
4  | 

So result need to be like this:

A  |  B
=======
1  | X
1  | Y
2  | 
3  | Z
4  | Z

Answer 1

You could use analytics:

SQL> WITH q1 AS (
  2     SELECT 1 a, 'X' b FROM DUAL UNION ALL
  3     SELECT 2 a, ''  b FROM DUAL UNION ALL
  4     SELECT 3 a, ''  b FROM DUAL UNION ALL
  5     SELECT 4 a, 'Z' b FROM DUAL
  6  ), q2 AS (
  7     SELECT 1 a, 'Y' b FROM DUAL UNION ALL
  8     SELECT 2 a, ''  b FROM DUAL UNION ALL
  9     SELECT 3 a, 'Z' b FROM DUAL UNION ALL
 10     SELECT 4 a, ''  b FROM DUAL
 11  )
 12  SELECT a, b
 13    FROM (SELECT a, b,
 14                 rank() over(PARTITION BY a 
 15                             ORDER BY decode(b, NULL, 2, 1)) rnk
 16             FROM (SELECT * FROM q1
 17                    UNION
 18                   SELECT * FROM q2))
 19   WHERE rnk = 1;

         A B
---------- -
         1 X
         1 Y
         2 
         3 Z
         4 Z