SQL & PL/SQL :: Generate Hourly Based Number Of Orders Placed Report

I have a table called 'orders' and having date and time of order placed in the field timeplaced. I need to generate a report which is having hourly based number of orders placed . If no order is placed in an hour then it should show 0 for that hour in the result .

create table orders (order_id integer, timeplaced date,last_updated date);
Insert into ORDERS
(ORDER_ID,
TIMEPLACED, LAST_UPDATED)
Values
(1, TO_DATE('10/11/2011 12:53:39', 'MM/DD/YYYY HH24:MI:SS'), TO_DATE('10/11/2011 10:53:39', 'MM/DD/YYYY HH24:MI:SS'));
[code]........

But I need the result for all the 24 hours. Actually row for the hour 1,2,3,4,5,6,8,9,13-23 are not present in the DB

TO_CHAR(TIMEPLACED,'HH')COUNT(*)

00
10
20
30
40
50
60
71
80
90
102
111
122
130
140
150
160
170
180
190
200
210
220
230