帮助在Ruby on Rails中对记录进行排序

Question

I have a score table that contains two columns: user_id and score

user_id score
1 200
1 120
1 230
2 300
2 345
3 100
3 40
4 350
4 500
......

Score.order('score DESC').limit(3) lists the top 3 scores. Instead, how would I get the top 3 scores where each user only gets one spot on the list (their highest score).

The high scores from the above table would be:

user_id: 4 score: 500
user_id: 2 score: 345
user_id: 1 score: 230

Thanks!

Tim

Answer 1

您应该能够对查询进行分组：

Score.order('score DESC').group('user_id').limit(3)

Answer 2

Score.all(:order => 'score DESC', :limit => 3, :group => :user_id)

随着新的Arel：

Score.group(:user_id).order('score DESC').limit(3)