我有一个表相关性，其中有2个列。 1. User_id（它有两个用户，一个和两个） 2.评级
*现在我想知道两个用户的评分之间的差异（1,2）。评级差异应为两个。 *
表：
“+--------------------------+
| Tables_in_ndcg_reporting |
+--------------------------+
| averages |
| last_visited_queries |
| products |
| queries |
| query_types |
| ratings |
| ratings_news |
| relevancies |
| schema_migrations |
| sites |
| users |
+--------------------------+
内部相关性：
`+-----+--------+------------+----------+---------+---------------------+---------------------+
| id |评级| product_id | query_id | user_id | created_at | updated_at
| 726 | 5 | 1 | 1 | 2 | 2016-11-24 06:06:12 | 2016-11-24 12:43:07 |
| 727 | 5 | 2 | 1 | 2 | 2016-11-24 06:06:12 | 2016-11-24 12:43:21 |
| 728 | 5 | 3 | 1 | 2 | 2016-11-24 06:06:12 | 2016-11-24 12:43:31 |
| 729 | 5 | 4 | 1 | 2 | 2016-11-24 06:06:12 | 2016-11-24 12:43:32 |
| 730 | 4 | 5 | 1 | 2 | 2016-11-24 06:06:12 | 2016-11-24 12:43:53 |
| 731 | 5 | 6 | 1 | 2 | 2016-11-24 06:06:12 | 2016-11-24 12:43:55 |
| 732 | 4 | 7 | 1 | 2 | 2016-11-24 06:06:12 | 2016-12-28 10:25:52 |
| 733 | 4 | 8 | 1 | 2 | 2016-11-24 06:06:12 | 2016-12-27 12:44:24 |
| 734 | 5 | 9 | 1 | 2 | 2016-11-24 06:06:12 | 2016-11-24 12:44:01 |
| 735 | 4 | 10 | 1 | 2 | 2016-11-24 06:06:12 | 2016-12-28 10:25:53 | `
答案 0 :(得分：0)
您可能正在寻找自我加入，如下所示：
select a.product_id
from relevencies a inner join relevencies b
on a.product_id = b.product_id and a.user_id <> b.user_id and a.rating >= (b.rating + 2);
如果用户只能对产品进行一次审核，则可以删除a.user_id <> b.user_id条件。