稍微解释下：
先把要唯一的字段(我这里是licenseID)用group把多于1个的数据找出来做为b表，同时把最小的ID选中，然后于原表a表关联，把大于最小ID的数据删除。

delete hxtable as a from hxtable a,
(
select licenseID,min(id) as id from hxtable group by licenseID having count(*) > 1
) as b
where a.licenseID = b.licenseID and a.id > b.id

同理，如果要保留最新的ID，可以这样写：

delete hxtable as a from hxtable a,
(
select licenseID,max(id) as id from hxtable group by licenseID having count(*) > 1
) as b
where a.licenseID = b.licenseID and a.id < b.id