S pomocí Delete with Join in MySQL
Udělal jsem
DELETE FROM table_name a
INNER JOIN (SELECT count(name) as dupesPostMillenia, name
FROM table_name
WHERE dob>'1/1/00'
GROUP BY name ) b on a.name=b.name
WHERE a.dob < '1/1/00' and b.dupesPostMillenia=0
Myslím, že by to mohlo pomoci.