How to make query for room reservation

Hello Folks,

I have these two tables
<code>
CREATE TABLE room
(
room_number numeric(9) not null,
room_type varchar(20) not null,
room_fare numeric(9, 2) not null,
room_description varchar(255) not null,

CONSTRAINT room_number_pk PRIMARY KEY (room_number)
);

CREATE TABLE room_reservation
(
room_reservation_id varchar(20) not null,
room_number numeric(9) not null,
client_username varchar(20) not null,
room_reservation_start_date date not null,
room_reservation_end_date date not null,
room_reservation_status varchar(20) not null,

CONSTRAINT room_reservation_id_pk PRIMARY KEY (room_reservation_id),
CONSTRAINT fk_room_number FOREIGN KEY (room_number) REFERENCES room(room_number),
CONSTRAINT fk_client_username FOREIGN KEY (client_username) REFERENCES client(client_username)
);

</code>
I want to make a query to check if a room is reserved for a particular date or not.

Suppose a room is reserved from 22nd April 2012 to 24rd April 2012, then if I check room availability

From 27th April 2012 to 30 April 2012 then result = room available
From 21th April 2012 to 23 April 2012 then result = room not available
From 19th April 2012 to 22 April 2012 then result = room not available

I tried to make this query lot but i am not getting success, little help will also work.

Thanks,

Jimmy