當鞋子合腳時....

一個 table 對另兩個 table 皆為一對多的關係。如果在一個查詢裡，要算出主表在兩個副表中的筆數，語法如下： @hot_tags = Tag.find(:all, :select => "tags.*, count(question_tags.id) as tags_q_count, + count(group_tags.id) as tags_g_count, (count(question_tags.id) + count(group_tags.id)) as tags_count", :group => "question_tags.tag_id", :joins => "left join question_tags on question_tags.tag_id = tags.id left join group_tags on group_tags.tag_id = tags.id", :order => "tags_count desc", :limit => 10)