Anda dapat membuat hourly
tabel, dan lakukan LEFT JOIN
create table hourly
(
/* hour is not a reserved keyword */
hour smallint(2) not null default 0
);
insert into hourly values (0),(1).... until 24
SELECT
hourly.hour,
COALESCE(COUNT(activities),0) AS "No of Activities"
FROM hourly
LEFT JOIN tbl1 ON hourly.hour=hour(tbl1.TimeStamp)
WHERE
tbl1.timestamp>=DATE_SUB(NOW(), INTERVAL 24 HOUR) AND
tbl1.Name=?
GROUP BY hourly.hour
ORDER BY hourly.hour;