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 work provided that your URL_ID column is unique.

DELETE FROM url WHERE URL_ID IN (
SELECT URL_ID
FROM url a INNER JOIN (
    SELECT URL_ADDR, MAX(URL_ID) MaxURLId 
    FROM url
    GROUP BY URL_ADDR
    HAVING COUNT(*) > 1) b ON a.URL_ID <> b.MaxURLId AND a.URL_ADDR = b.URL_ADDR
)