SQL 逻辑：

1. 首先找出所有重复的sku_id
2. 在找出这些sku_id中关联的主键id最大的一条记录(用来保留，不删除)
3. 两个sql合并 就可以筛选出来最终需要删除的id

select id from ​​sku_and_goods_sign​​​ where sku_id in (select sku_id from ​​sku_and_goods_sign​​​ group by sku_id having count(1) > 1) and id not in (select max(id) from ​​sku_and_goods_sign​​ group by sku_id having count(1) > 1)