I want to left join payments y with orders o on y.orderid=o.orderid

so, you mean either:

select *, case when resultcode = 'Canceled' then 'Payment Processed' when resultcode = 'Completed' then 'Payment Processed' when resultcode = 'confirmed' then 'Payment Processed' when resultcode = 'Denied' then 'Payment Processed' when resultcode = 'Pending' then 'Payment Processed' when resultcode = 'unconfirmed' then 'Payment Processed' when resultcode = '' and (debit is null or ISNUMERIC(debit) = 0 or cast(debit as money) >=0) then 'Payment Processed' when resultcode = '' and debit is not null and ISNUMERIC(debit) = 1 and CAST(debit as money)<0 then 'Refunded' when resultcode = 'Canceled_Reversal' then 'Refunded' when resultcode = 'Reversed' then 'Refunded' end as resultcodetype ,debit - convert(money, paymentfee) as 'netamount' 
from payments p
left join orders o
  on  y.orderid=o.orderid
where p.dateentered between '03/01/2011' and '03/09/2011' 
order by p.dateentered desc 

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but that seems "trivial" as question ...

so, possibly this:

select *, case when resultcode = 'Canceled' then 'Payment Processed' when resultcode = 'Completed' then 'Payment Processed' when resultcode = 'confirmed' then 'Payment Processed' when resultcode = 'Denied' then 'Payment Processed' when resultcode = 'Pending' then 'Payment Processed' when resultcode = 'unconfirmed' then 'Payment Processed' when resultcode = '' and (debit is null or ISNUMERIC(debit) = 0 or cast(debit as money) >=0) then 'Payment Processed' when resultcode = '' and debit is not null and ISNUMERIC(debit) = 1 and CAST(debit as money)<0 then 'Refunded' when resultcode = 'Canceled_Reversal' then 'Refunded' when resultcode = 'Reversed' then 'Refunded' end as resultcodetype ,debit - convert(money, paymentfee) as 'netamount' 
from orders o
left join payments p
  on  y.orderid=o.orderid
 and p.dateentered between '03/01/2011' and '03/09/2011' 
order by p.dateentered desc 

Select all Open in new window

but that does not make sense to apply left join.
either you want all orders with payments in that date range (inner join), or all order made in that date range, even if there is no payments (at all. ..)

so, something like:

select *, case when resultcode = 'Canceled' then 'Payment Processed' when resultcode = 'Completed' then 'Payment Processed' when resultcode = 'confirmed' then 'Payment Processed' when resultcode = 'Denied' then 'Payment Processed' when resultcode = 'Pending' then 'Payment Processed' when resultcode = 'unconfirmed' then 'Payment Processed' when resultcode = '' and (debit is null or ISNUMERIC(debit) = 0 or cast(debit as money) >=0) then 'Payment Processed' when resultcode = '' and debit is not null and ISNUMERIC(debit) = 1 and CAST(debit as money)<0 then 'Refunded' when resultcode = 'Canceled_Reversal' then 'Refunded' when resultcode = 'Reversed' then 'Refunded' end as resultcodetype ,debit - convert(money, paymentfee) as 'netamount' 
from orders o
left join payments p
  on  y.orderid=o.orderid
where o.dateentered between '03/01/2011' and '03/09/2011' 
order by o.dateentered desc 

Select all Open in new window

note that the WHERE clause now checks on orders table date column

hope this helps