You could do this:
SELECT
*
FROM
(
SELECT
ORDERID ,
clientnum,
ID,
READYDATE,
(
case when ID=56 then 'O'
ELSE
CASE when ID=65 then 'A'
ELSE
'NONE'
END
END) AS LOctaion
from orde_
) AS tbl
where tbl.READYDATE='2014-05-09' AND tbl.LOctaion='A'