Avoiding duplicate entries in query

[S3NTIN3L]

I am making a dating website where people can see if people have viewed their profile.

To do this I use a query to insert an entry into a two field table - id and viewed_by.

This is the query I use:

mysql_query("INSERT INTO viewed_me (id, viewed_by) VALUES($id, $user_id)");

It works but it is possible for the same user to view another users profile twice therefore on the viewed me page you get two of the same user shown which is not right.

I have had problems using a primary key in the table - it messes it up.
Is there anyway I can add more code to this query, like an if statement to make sure a duplicate entry is not going to be made?

Thanks anyone

[dagon]

add a unique key on id, viewed_by

so if both are the same it wont insert.

ALTER TABLE viewed_me ADD UNIQUE stop_dupes ( id, viewed_by )

[bradgrafelman]

I would think a primary key is more appropriate than a unique key here.

@: You claim that a primary key "messes it up" - what does that mean? How did you add the primary key?