DESCRIBE tab1;
DESCRIBE tab2;

CREATE TABLE test_minus
AS
select 'TAB-1' AS tab, a,b,c,d from tab1 where b = 123
UNION
select 'TAB-2',a,b,c,d from tab2 where b = 123;

DESCRIBE test_minus;

SELECT tab, COUNT(*)
FROM test_minus
GROUP BY tab;

SELECT a,b,c,d FROM test_minus WHERE tab = 'TAB-1'
MINUS
SELECT a,b,c,d FROM test_minus WHERE tab = 'TAB-2';

SQL> CREATE TABLE t_char(c CHAR(10));
Table T_CHAR created.

SQL> CREATE TABLE t_vc2(vc2 VARCHAR2(10));
Table T_VC2 created.

SQL> DESCRIBE t_char;
Name Null? Type     
---- ----- -------- 
C         CHAR(10) 

SQL> DESCRIBE t_vc2;
Name Null? Type         
---- ----- ------------ 
VC2        VARCHAR2(10) 

SQL> INSERT INTO t_char(c) VALUES('test');
1 row inserted.

SQL> INSERT INTO t_vc2(vc2) VALUES('test');
1 row inserted.

SQL> COMMIT;
Commit complete.

SQL> SELECT c FROM t_char
  2  MINUS
  3  SELECT vc2 FROM t_vc2;

C         
----------
test      

SQL> SELECT '"' || c || '"' as c FROM t_char;

C           
------------
"test      "

SQL> SELECT '"' || vc2 || '"' as vc2 FROM t_vc2;

VC2         
------------
"test"