1. 양쪽 테이블의 기준컬럼을 중심으로 집계컬럼이 동일한 경우

WITH 
A AS
   (SELECT 'A' AS CODE, 8 AS QTY FROM DUAL 
    UNION ALL
    SELECT 'A' AS CODE, 2 AS QTY FROM DUAL 
    UNION ALL
    SELECT 'B' AS CODE, 7 AS QTY FROM DUAL 
    UNION ALL
    SELECT 'D' AS CODE, 9 AS QTY FROM DUAL)
, B AS
   (SELECT 'A' AS CODE, 8 AS QTY FROM DUAL 
    UNION ALL
    SELECT 'C' AS CODE, 7 AS QTY FROM DUAL 
    UNION ALL
    SELECT 'C' AS CODE, 2 AS QTY FROM DUAL 
    UNION ALL
    SELECT 'D' AS CODE, 9 AS QTY FROM DUAL)

SELECT  T.CODE
,       SUM(T.QTY) AS QTY
FROM   (SELECT  CODE
        ,       QTY  
        FROM A 

        UNION ALL 

        SELECT  CODE
        ,       QTY 
        FROM B) T
GROUP BY T.CODE
ORDER BY T.CODE;



CODE                                    QTY
-------------------------------- ----------
A                                        18 
B                                         7 
C                                         9 
D                                        18 

2. 양쪽 테이블의 기준컬럼을 중심으로 집계컬럼이 상이한 경우

WITH 
A AS
   (SELECT 'A' AS CODE, 8 AS QTY FROM DUAL 
    UNION ALL
    SELECT 'A' AS CODE, 2 AS QTY FROM DUAL 
    UNION ALL
    SELECT 'B' AS CODE, 7 AS QTY FROM DUAL 
    UNION ALL
    SELECT 'D' AS CODE, 9 AS QTY FROM DUAL)
, B AS
   (SELECT 'A' AS CODE, 8 AS QTY FROM DUAL 
    UNION ALL
    SELECT 'C' AS CODE, 7 AS QTY FROM DUAL 
    UNION ALL
    SELECT 'C' AS CODE, 2 AS QTY FROM DUAL 
    UNION ALL
    SELECT 'D' AS CODE, 9 AS QTY FROM DUAL)

SELECT  T.CODE
,       SUM(T.A_QTY)    AS A_QTY
,       SUM(T.B_QTY)    AS B_QTY
FROM   (SELECT  CODE
        ,       QTY             AS A_QTY
        ,       TO_NUMBER(NULL) AS B_QTY 
        FROM A 

        UNION ALL

        SELECT  CODE
        ,       TO_NUMBER(NULL) AS A_QTY
        ,       QTY             AS B_QTY 
        FROM B) T
GROUP BY T.CODE
ORDER BY T.CODE;




CODE                                  A_QTY      B_QTY
-------------------------------- ---------- ----------
A                                        10          8 
B                                         7            
C                                                    9 
D                                         9          9