Are you looking to find rows where:

A). the primary key is different, but all the rest of the data is the same (so a row from table1 is related to a row in table2).

Code:
15:01:53 SQL> create table temp_table1 (cust_num number(4),
15:03:03   2  favourite_colour varchar2(10),
15:03:03   3  favourite_car varchar2(10),
15:03:03   4  constraint temp_table1_pk 
15:03:03   5  primary key (cust_num));

Table created.

15:03:40 SQL> create table temp_table2 (cust_num number(4),
15:03:50   2  favourite_colour varchar2(10),
15:03:50   3  favourite_car varchar2(10),
15:03:50   4  constraint temp_table2_pk 
15:03:50   5  primary key (cust_num));

Table created.

15:20:06 SQL> select * from temp_table1;

  CUST_NUM FAVOURITE_ FAVOURITE_
---------- ---------- ----------
         1 red        porsche
         2 blue       ferrari
         4 orange     Skoda

15:20:19 SQL> select * from temp_table2;

  CUST_NUM FAVOURITE_ FAVOURITE_
---------- ---------- ----------
         1 red        porsche
         3 blue       ferrari
         5 orange     Beetle

15:20:39 SQL> select a.*, b.*
15:20:57   2  from (select * from temp_table1 where cust_num not in(
15:20:57   3   select cust_num from temp_table2)) a,
15:20:57   4       (select * from temp_table2 where cust_num not in(
15:20:57   5   select cust_num from temp_table1)) b
15:20:57   6  where a.favourite_colour=b.favourite_colour
15:20:57   7   and a.favourite_car=b.favourite_car;

  CUST_NUM FAVOURITE_ FAVOURITE_   CUST_NUM FAVOURITE_ FAVOURITE_
---------- ---------- ---------- ---------- ---------- ----------
         2 blue       ferrari             3 blue       ferrari

15:20:58 SQL>
or are you looking for:

B). Any row that that is in one table, but not in the other and the rows bear no relation to each other?...