SQL> create table test
  2  (id number,
  3   name varchar2(20)
  4  );

Table created.

SQL> create unique index iun_test on test (id, name);

Index created.

SQL> insert into test (id, name) values (1, 'Little');

1 row created.

SQL> insert into test (id, name) values (1, null);

1 row created.

SQL> insert into test (id, name) values (1, null);
insert into test (id, name) values (1, null)
*
ERROR at line 1:
ORA-00001: unique constraint (SCOTT.IUN_TEST) violated


SQL> insert into test (id, name) values (2, null);

1 row created.

SQL> select * from test order by id;

        ID NAME
---------- --------------------
         1 Little
         1                
         2

SQL>

select * from sapr3.T156T a 
where a.MANDT='001' 
AND a.BWART='551' 
AND  a.rowid > ANY (select b.ROWID from sapr3.T156T b 
                    where a.MANDT=b.MANDT 
                    AND a.SPRAS=b.SPRAS 
                    AND a.BWART=b.BWART 
                    AND a.SOBKZ=b.SOBKZ 
                    AND a.KZBEW=b.KZBEW 
                    AND a.KZZUG=b.KZZUG 
                    AND a.KZVBR=b.KZVBR 
                    AND a.BTEXT=b.BTEXT
                   );


MANDT     SPR BWART     SOB KZB KZZ KZV
--------- --- --------- --- --- --- ---
BTEXT
------------------------------------------------------------
001       C   551       Q
VM sezarotov. proj.

001       C   551       Q
VM sezarotov. proj.

001       C   551       Q
VM sezarotov. proj.

001       C   551       Q
VM sezarotov. proj.

001       C   551       Q
VM sezarotov. proj.

analyze table sapr3.T156T validate structure;
  Table analyzed.
analyze table sapr3.T156T validate structure cascade;
  ORA-01499: table/index cross reference failure - see trace file