Advice indexing new DB

[bob bob]

Hi,

I have a new test DB with my firewall logs in it. Fairly simple but a lot of records.

mysql> desc logs;
+-----------+------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-----------+------------+------+-----+---------+-------+
| fw_name | char(20) | YES | | NULL | |
| date | date | YES | | NULL | |
| time | time | YES | | NULL | |
| event | char(20) | YES | | NULL | |
| ip1 | bigint(20) | YES | | NULL | |
| userid | char(10) | YES | | NULL | |
+-----------+------------+------+-----+---------+-------+
6 rows in set (0.00 sec)

There are 20 million records! It works for what I want it for, but I am conscious that I don't have any primary key or indexing. I have gotten myself all confused on what to do for the best.

Do I need to define a primary key or an index? I would generally want to search on a combination of date and userid.

Thanks