SQL案例：根据二度人脉推荐好友

根据二度人脉推荐好友

DROP TABLE IF EXISTS FRIEND;
create table friend(
    uid              bigint not null comment '用户标识',
    friend_uid       bigint not null comment '申请加为好友的用户标识',
    sys_create_date  datetime not null comment '申请时间',
    sys_last_update  datetime not null comment '更新时间',
    state            tinyint not null comment '好友状态 0 ： 删除, 1:申请好友, 2 : 好友',
    primary key(uid, friend_uid)
)ENGINE=InnoDB DEFAULT CHARSET=utf8 COMMENT '好友表';

uid为当前用户的ID，查找id为13的用户查询二度人脉好友

SELECT friend_uid 
FROM friend 
WHERE state=2 
      and uid in 
         (select friend_uid from friend where uid=13 and state=2) 
    and friend_uid not in 
        (select friend_uid from friend where uid=13 ) 
    and friend_uid != 13 
limit 6