What is wrong with the query?

Question

Hi
I have a below query. When I parse the query, It did not parsed. Could you please tell me where is the issue?

declare @row_number int
declare @acct_no bigint
declare @channel_name nvarchar

SET @row_number=0
select
c.Account_Id,
c.Channel_Name,
c.Last_Refresh_Time
from
(
select
@row_number=CASE WHEN @acct_no = b.Account_Id and @channel_name = b.Channel_Name
THEN @row_number + 1
ELSE 1
END AS rnk,
@acct_no= b.Account_Id as Account_Id,
@channel_name= b.Channel_Name as Channel_Name,
b.Last_Refresh_Time
from
(
select
a.Account_Id,
a.Channel_Name,
a.Last_Refresh_Time
from
(
select
a.acct_id as Account_Id,
dp.name as Channel_Name,
dc.last_call_made_for_access As Last_Refresh_Time
from
stg.delivered_cap dc
inner join stg.ordered_product tp on
tp.ord_prod_id=dc.ord_prod_id
inner join stg.acct_order_item ai on
tp.ord_prod_id = ai.ord_prod_id
inner join stg.acct_order ao on
ai.order_id = ao.order_id
inner join stg.account a on
ao.acct_id = a.acct_id
left join stg.delivery_point dp on
dp.del_point_id = dc.del_point_id
left join stg.account_status dcact on
dcact.acct_stat_id=dc.acct_status_id
where
a.bu_id = 49
and dc.last_call_made_for_access is not null
) a
order by Last_Refresh_Time desc
) b
) c
where
c.rnk=1