SQL Query to find missing rows between two related tables

SELECT A.ABC_ID, A.VAL WHERE NOT EXISTS 
   (SELECT * FROM B WHERE B.ABC_ID = A.ABC_ID AND B.VAL = A.VAL)

or

SELECT A.ABC_ID, A.VAL WHERE VAL NOT IN 
    (SELECT VAL FROM B WHERE B.ABC_ID = A.ABC_ID)

or

SELECT A.ABC_ID, A.VAL LEFT OUTER JOIN B 
    ON A.ABC_ID = B.ABC_ID AND A.VAL = B.VAL WHERE B.VAL IS NULL