create table source_table ( 
header_id  number, line_id   number, account_type   varchar2(30),       accrual_tier   varchar2(30) 
)

insert into source_table values (101   ,       1         ,'expense'                ,NULL)

insert into source_table values (101   ,       2         ,'liability'              ,'TAX')

insert into source_table values (102   ,       1        ,'liability'               ,'C'||chr(38)||'B')

insert into source_table values (102   ,       2         ,'expense'                ,NULL)

insert into source_table values (102   ,       3         ,'expense'                ,NULL)

select header_id 
      , line_id 
      , account_type 
      , accrual_tier 
      , max(case when account_type = 'liability' then  accrual_tier end) over (partition by header_id) as sub_accrual 
from source_table 
order by header_id 
      , line_id 

select header_id
      , line_id
      , account_type
      , accrual_tier
      , first_value (accrual_tier ignore nulls) over (partition by header_id order by account_type desc) as sub_accrual
from source_table
order by header_id
      , line_id
/