oracle 删除重复数据

我要删除2015-10-19日的wdinfo字段重复的数据

（1）先查出数据

SELECT id, wdinfo
FROM BUSINISS
where starttime = to_date('2015-10-19', 'yyyy-mm-dd')
order by id desc

（2）查出这些重复数据的重复次数

select min(id)，count(*)  from (SELECT id, wdinfo
FROM BUSINISS
where starttime = to_date('2015-10-19', 'yyyy-mm-dd')
order by id desc) group by wdinfo 

(3)最后留下最小id的数据，其他的重复数据删除

delete from businiss where id not in (select min(id) from (SELECT id, wdinfo

FROM BUSINISS
where starttime = to_date('2015-10-19', 'yyyy-mm-dd')
order by id desc) group by wdinfo )