Remove duplicates using only a MySQL query?

Question

I have a table with the following columns:

URL_ID    
URL_ADDR    
URL_Time

I want to remove duplicates on the URL_ADDR column

Answer 1

This will leave the ones with the highest URL_ID for a particular URL_ADDR

DELETE FROM table
WHERE URL_ID NOT IN 
    (SELECT ID FROM 
       (SELECT MAX(URL_ID) AS ID 
        FROM table 
        WHERE URL_ID IS NOT NULL
        GROUP BY URL_ADDR ) X)   /*Sounds like you would need to GROUP BY a 
                                   calculated form - e.g. using REPLACE to 
                                  strip out www see Daniel's answer*/

(The derived table 'X' is to avoid the error "You can't specify target table 'tablename' for update in FROM clause")