create table t ( c1 number , c2 varchar2(10) , c3 varchar2(10) ); insert into t values( 1, 'A' , 'A' ); insert into t values( 2, 'A' , 'B' ); insert into t values( 3, null , 'A' ); insert into t values( 4, null , null ); commit; set null '(null)' set numformat 99 set serveroutput on