mysql time comparison - strange result

I use a timestamp field that is set with current time when inserts.

It has the following entries.

    6   2011-02-10 09:36:31     174.129.228.67
    4   2011-02-10 09:36:36     174.129.228.67
    5   20开发者_高级运维11-02-10 09:36:41     174.129.228.67
    4   2011-02-10 12:11:08     192.168.0.4
    6   2011-02-10 12:48:21     192.168.0.22
    1   2011-02-10 12:48:45     192.168.0.22
    2   2011-02-10 12:49:00     192.168.0.22
    2   2011-02-10 12:49:01     66.220.158.251
    6   2011-02-10 12:49:18     66.220.158.251
    5   2011-02-10 13:00:25     66.220.149.249

Now() is

2011-02-10 17:20:04

When I execute, select * from list where timestampField > (now()-(8*60*60))

It return empty result set. Here, I expect entries entered after 2011-02-10 9:20:04.

When I execute, select * from list where timestampField > (now()-(14*60*60))

I get,

1   2011-02-10 12:48:45     192.168.0.22
2   2011-02-10 12:49:00     192.168.0.22
2   2011-02-10 12:49:01     66.220.158.251
6   2011-02-10 12:49:18     66.220.158.251

Why this. Could you tell me what is the proper way to get entries of previous hours.

Thanks.

You cannot subtract seconds from time in mysql. You need to use a function like this:

WHERE dateadded > DATE_SUB(NOW(), INTERVAL 8 HOUR)