亚马逊云科技技术品牌专区

主键	关注者id	被关注者id
1	1	2
2	1	3
3	2	1
4	2	3
5	3	1
6	3	4
7	4	3
8	5	6
9	7	8

先建一张好友关系表

CREATE TABLE IF NOT EXISTS `follower` (
  `id` int(6) unsigned NOT NULL,
  `user_id` varchar(200) NOT NULL,
  `follower_id` varchar(200) NOT NULL,
  PRIMARY KEY (`id`)
) DEFAULT CHARSET=utf8;
INSERT INTO `follower` (`id`, `user_id`, `follower_id`) VALUES
  ('1', '1', '2'),
  ('2', '1', '3'),
  ('3', '2', '1'),
  ('4', '2', '3'),
  ('5', '3', '1'),
  ('6', '3', '4'),
  ('7', '4', '3'),
  ('8', '5', '6'),
  ('9', '7', '8');

　　我关注的人

select * from follower where user_id = '1'

 　　关注我的人

select * from follower where  follower_id = '1' 

　　跟我互关的人

select a.user_id from follower as a inner join follower as b
on a.follower_id = '1' and b.follower_id = '1'

　　但是运行上方代码，会有重复数据出现；

　　跟我互关的人去重

select a.* from (
  select a.user_id from follower as a inner join follower as b
  on a.follower_id = '1' and b.follower_id = '1'
) a group by a.user_id;

　　判断两人关系(互关)

select 1 from follower where user_id = '1' and follower_id = '2'
union all 
select 2 from follower where user_id = '2' and follower_id = '1'

这里会返回一个List<Integer> 数组，有四种情况

•      空数组 A,B 之前无任何关系
•      [1,2] "1" 和 "2"相互关注
•      [1]  "1" 关注了 "2"
•      [2]  "2" 关注了 "1"