Find duplicate records in MySQL

The key is to rewrite this query so that it can be used as a subquery.

SELECT firstname, 
   lastname, 
   list.address 
FROM list
   INNER JOIN (SELECT address
               FROM   list
               GROUP  BY address
               HAVING COUNT(id) > 1) dup
           ON list.address = dup.address;

SELECT date FROM logs group by date having count(*) >= 2

Why not just INNER JOIN the table with itself?

SELECT a.firstname, a.lastname, a.address
FROM list a
INNER JOIN list b ON a.address = b.address
WHERE a.id <> b.id

A DISTINCT is needed if the address could exist more than two times.