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.

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

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