timestamp in mysql

[GoGnaget]

Just for fun, I'm constructing a small community...
When someone logs in I register what time they logged in and saves the info in a database using the field:

Name: "latastlogin"
Type: timestamp(14)
Null: Yes

So when they log in I just make a call to mysql

UPDATE tablename SET latestlogin=NULL WHERE username='$global_username'

In the same table I got a field that looks like this:

Name: "latastaction"
Type: timestamp(14)
Null: Yes

I use that field to register when a user loads a new page. (I need that info so I know can log out people that have been inactive for too long)...
I use the same call here except that I changed "latestlogin" to "latestaction":

UPDATE tablename SET latestaction=NULL WHERE username='$global_username'

The problem is that when I make this call, for some reason, it also updates the "latestlogin"-field...
I've looked through the code billions of times even if the only call I make is:

UPDATE tablename SET latestaction=NULL WHERE username='$global_username'

It still updates the latestlogin field.

Just updating the latestlogin field and NOT the latestaction field works fine, but not the other way around...
The only way I got it working was if I ran the query like this:

UPDATE tablename SET latestlogin=latestlogin, latestaction=NULL WHERE username='$global_username'

But that's a disturbing "work-around"...

any ideas?

[[deleted]]

That is expected behavior with MySQL. The first timestamp field will auto update itself on any update to that row unless you set it back to itself. See:

http://www.mysql.com/doc/en/DATETIME.html

What you are doing to get around it is the the common method for handling it...