SQL> select * from a1;

	ID NAME

---------- ----------

	 1 a

	 1 a

	 2 a

	 3 a

SQL> select * from a2;

	ID

----------

	 2

	 3

	 2

SQL>  select * from a1 where id not in (select id from a2);

	ID NAME

---------- ----------

	 1 a

	 1 a

SQL> select a1.* from a1,a2

  2  where a1.id=a2.id(+)

  3  and a2.id is null;

	ID NAME

---------- ----------

	 1 a

	 1 a