Rails Rails4中使用left,rightouterjoin

参考：  https://stackoverflow.com/questions/24358805/left-outer-join-in-rails-4/24358839

注意：　可以在joins方法中增加ＳＱＬ语句，就可以了．　记得：　要指定外键的关联．　例如：　on a.fk_id = b.id

left outer join: 
User.joins('left outer join workers on workers.user_id = users.id')

right outer join: 
User.joins('right outer join workers on workers.user_id = users.id')