-- 检查重复code1
select count(identity) num, identity from event_log 
where code=‘code1‘ 
group by identity having count(identity) > 1
order by num desc

DELETE FROM event_log WHERE `code`=‘code1‘ AND identity IN (
    SELECT identity from (
        SELECT identity FROM event_log WHERE code=‘code1‘ GROUP BY identity HAVING count(identity) > 1
    ) a
) AND id NOT IN (
    SELECT keepId FROM (
        SELECT min(id) keepId FROM event_log WHERE code=‘code1‘ GROUP BY identity HAVING count(identity) > 1
    ) b
)