SQL> DROP TABLE ADVERSE_EVENT;
 
Table dropped
SQL> DROP TABLE MEDICATION;
 
Table dropped
SQL> CREATE TABLE Adverse_Event(Patient number, Event VARCHAR2(20));
 
Table created
SQL> INSERT INTO Adverse_Event values(100, 'Fever');
 
1 row inserted
SQL> INSERT INTO Adverse_Event values(100, 'Cold');
 
1 row inserted
SQL> INSERT INTO Adverse_Event values(100, 'Blood Pressure');
 
1 row inserted
SQL> CREATE TABLE medication(Patient number, Medicine varchar2(20),Event VARCHAR2(20));
 
Table created
SQL> INSERT INTO medication VALUES(100, 'PCM', 'Fever');
 
1 row inserted
SQL> INSERT INTO medication VALUES(100, 'Rantac', 'Acidity');
 
1 row inserted
SQL> INSERT INTO medication VALUES(100, 'domstal', 'Vomit');
 
1 row inserted
SQL> INSERT INTO medication VALUES(100, 'Storvas', 'Blood Pressure');
 
1 row inserted
SQL> COMMIT;
 
Commit complete
SQL> SELECT *
  2    FROM ADVERSE_EVENT
  3   WHERE EVENT NOT IN (SELECT EVENT FROM MEDICATION);
 
   PATIENT EVENT
---------- --------------------
       100 Cold

select * from adverse
where (patient, event) not in 
      (select patient, event from medication)
/

select * from adverse a
where not exists (select null from medication m
                  where m.patient = a.patient
                    and m.event = a.event)
/