Help me writing a query

[eluser]aryan_[/eluser]
I have a table like this-

Code:

---------------------------------------------
id | ad-id | user_id | datetime   | ip
---------------------------------------------
1  | 2     | 10      | 1248977229 | 127.0.0.1
---------------------------------------------
2  | 3     | 10      | 1248977329 | 127.0.0.1
---------------------------------------------
3  | 3     | 10      | 1251556503 | 127.0.0.1
---------------------------------------------
4  | 4     | 15      | 1251556603 | 127.0.0.1
---------------------------------------------

I want to get clicks made by a user per day with date. 'datetime' field is varchar, should I change it to MySql timestamp.

Thanks!