insert into c 
select 1, 10 ,'A' from dual union all
select 1 ,10, 'B' from dual union all
select 2, 20, 'A' from dual union all
select 3 ,30 ,'A' from dual union all
select 4 ,40, 'A' from dual union all
select 5 ,10 ,'A' from dual union all
select 6 ,30 ,'A' from dual union all
select 2 ,10 ,'B' from dual union all
select 4 ,40 ,'B' from dual union all
select 6 ,30 ,'C' from dual 

commit;


--select * from c

select distinct dt,
       type,
       price,
       decode(avg(price) over(partition by type order by dt range between 3
                   preceding and 1 preceding),
              null,
              price,
              avg(price) over(partition by type order by dt range between 3
                   preceding and 1 preceding)) as t
  from c