How to add Order by in sql query - sql

Question

update Room set Status = case
when Room_Rev.In_DateTime IS NOT NULL and Room_Rev.Out_DateTime IS NULL
then 'U'
when Room_Rev.In_DateTime IS NOT NULL and Room_Rev.Out_DateTime IS NOT NULL
then 'A'
when Room.Status!='R' and Room.Status!='U' and Room.Status!='A'
then Room.Status
else 'R'
end
FROM Room JOIN Room_Rev
ON Room.Room_ID=Room_Rev.Room_ID
and
((Room_Rev.Start_Date >= '2015-03-22' and Room_Rev.End_Date <= '2015-03-22')
OR
(Room_Rev.Start_Date<= '2015-03-22' and Room_Rev.End_Date> '2015-03-22')
OR
(Room_Rev.Start_Date< '2015-03-22' and Room_Rev.End_Date>= '2015-03-22'))
How to add order by Rev_ID desc in the query?
There are two table which is Room and Room_Rev,
they are one to many relationship
The last two row ROM0006 already fill the In_DateTime and Out_DateTime,
thus it regard check out,
and the last row insert new reservation,
the In_DateTime is null
thus i need the query return 'R' (Reserved status)

Answer 1

As one of the possible solutions I suggest a nested query instead of a join in UPDATE statement. The logic of the update is not completely clear to me, so I leave the final update for OP to correct order of sorting (Note I used top 1 and order by room_ID in the nested SELECT statement). However, this approach allows to handle all usual techniques applicable for a SELECT.
update Room set Status = (select TOP 1 case
when Room_Rev.In_DateTime IS NOT NULL and Room_Rev.Out_DateTime IS NULL
then 'U'
when Room_Rev.In_DateTime IS NOT NULL and Room_Rev.Out_DateTime IS NOT NULL
then 'A'
when Room.Status!='R' and Room.Status!='U' and Room.Status!='A'
then Room.Status
else 'R'
end
FROM Room_Rev
WHERE Room.Room_ID=Room_Rev.Room_ID
and
((Room_Rev.Start_Date >= '2015-03-22' and Room_Rev.End_Date <= '2015-03-22')
OR
(Room_Rev.Start_Date<= '2015-03-22' and Room_Rev.End_Date> '2015-03-22')
OR
(Room_Rev.Start_Date< '2015-03-22' and Room_Rev.End_Date>= '2015-03-22'))
ORDER BY Room_Rev.Room_Id
)
PS. As a piece of advise I still assume that such approach is not valid. It prevents proper normalization of data. You'd rather have this information always queried dynamically when required, instead of writing static value to ROOM.status