UNION query question
Sum after you did the union (hope DB2 does it this way):

SELECT  BRAND, BRAND_GROUP, SUB_BRAND, SUM(INCOME) AS TOTAL_INCOME
FROM    (SELECT BRAND, BRAND_GROUP, SUB_BRAND, INCOME
         FROM   "tema".MMT
         WHERE  BRAND_GROUP IS NULL
         AND    SUB_BRAND IS NULL
         UNION ALL
         SELECT BRAND, BRAND_GROUP, SUB_BRAND, INCOME
         FROM   "tema".BGT
         WHERE  BRAND_GROUP IS NULL
         AND    SUB_BRAND IS NULL) AS T
GROUP BY BRAND, BRAND_GROUP, SUB_BRAND;


Just a question. Why do you need the BRAND_GROUP and SUB_BRAND (since they are both NULL)?