SQL> declare
  2  v_num1 NUMBER := &sv_num1;
  3  v_num2 NUMBER := &sv_num2;
  4  v_num3 NUMBER := &sv_num3;
  5  v_result NUMBER;
  6  
  7  begin
  8  v_result := CASE
  9  WHEN v_num1 IS NOT NULL THEN v_num1
 10  ELSE
 11  CASE WHEN v_num2 IS NOT NULL THEN v_num2
 12  ELSE v_num3
 13  END
 14  END;
 15  DBMS_OUTPUT.PUT_LINE ('Result: ' ||v_result);
 16  END;
 17  /
Enter value for sv_num1: 1
Enter value for sv_num2: 1
Enter value for sv_num3: 1
Result: 1

PL/SQL procedure successfully completed.