Supongan se que en esta este codigo
SELECT B.ID_B, B.COSTO, A.ID_A, A.COSTO
FROM TABLA_B AS B
INNER JOIN TABLA_A AS A
ON A.ID_A = B.ID_B
UNION ALL
SELECT 0,
0,
0,
3;
En lugar de eso quiero esto
SELECT B.ID_B, B.COSTO, A.ID_A, A.COSTO
FROM TABLA_B AS B
INNER JOIN TABLA_A AS A
ON A.ID_A = B.ID_B
UNION ALL
SELECT 0,
0,
0,
B.ID_B;