Rails SQL INTERSECT无法正常工作

Question

我希望得到一个用户的共同朋友，即我关注的人并跟着我回来：

# get users I'm following
following_ids = "SELECT followed_id FROM relationships WHERE follower_id = #{self.id}"

# get user that are following me
follower_ids = "SELECT follower_id FROM relationships WHERE followed_id = #{self.id}"

User.where("id IN (#{following_ids} INTERSECT #{follower_ids})")

但是，我收到以下错误：

  

Mysql2 ::错误：您的SQL语法中有错误;检查手册   对应于您的MySQL服务器版本，以获得正确的语法   使用near＆＃39; INTERSECT SELECT follower_id FROM relationships WHERE   followed_id = 2））＆＃39;第1行：SELECT users。* FROM users WHERE（id   IN（SELECT followed_id FROM relationships WHERE follower_id = 2   INTERSECT SELECT follower_id FROM relationships WHERE followed_id =   2））

单个查询确实有效，所以我知道INTERSECT关键字存在问题。

Answer 1

MySQL没有INTERSECT。有关详细信息，请参阅here，here或here。