How to remove duplicated records from a MySQL table?

I would be grateful if you could help me to solve this sql problem.

I have a table that contains two columns. Name them UserID and LocationID in this example.

I would like to clean this table, so I would like to keep the first occurences of each unique pairs of UserIDs and LocationIDs and delete additional rows that contains the same pairs. In other words I would like to know every location for each user where he has been to. If he visited the same place again and again and it was logged, I would like to delete those records. For example, this is the original table:

ID UserID  LocationID
1. "user1" "location1"
2. "user1" "location2"
3. "user2" "location3"
4. "user1" "location1"
5. "user2" "location3"
6. "user2" "location3"

I would like to remove the 4., 5. and 6. rows.

Is it possible to solve it in one mysql command?
Thanks.

Answer

Delete using a self-join:

DELETE t2.*
FROM tablename AS t1
INNER JOIN tablename AS t2

    ON t1.UserID = t2.UserID
    AND t1.LocationID = t2.LocationID
WHERE t1.ID < t2.ID

tablename should be replace with the name of your table.