SELECT count(*) FROM VW_STG_CONTRACTS A 
WHERE NOT EXISTS (SELECT V_ENTITY_CODE FROM VW_FCT_INFO B WHERE A.V_LV_CODE=B.V_ENTITY_CODE)

count(*)
32198

SELECT count(*) FROM VW_STG_CONTRACTS A 
WHERE A.V_LV_CODE NOT IN (SELECT V_ENTITY_CODE FROM VW_FCT_INFO B )

count(*)
0

SQL> select * from dual where dummy not in ('Y','Z');
D
-
X

1 row selected.

SQL> select * from dual where dummy not in ('Y','Z',null);

no rows selected