select a.* 
from 表结构如下 a inner join 表结构如下 b on a.goods_id=b.goods_id
where a.category_id=3 and b.category_id=4

------解决方案--------------------

select goods_id,count(*)
from (
 select goods_id,category_id
 from mytable
 group by goods_id,category_id
) r
group by goods_id
having count(*)>1;