PostgreSQL：
User.count(:order => 'DATE(created_at) DESC', :group => ["DATE(created_at)"])
User.count(:order => 'DATE(created_at) DESC', :group => ["DATE(created_at)"]).each {|u| puts "#{u[0]} -> #{u[1]}" }
Foo.order("DATE(start_at)").group("DATE(start_at)").count
Mysql在另一篇，heroku啊，让我学习postgresql
select floor(datediff(now(), created) / 3) * 3 as days_ago ,min(created) ,max(created) ,count(*) from t1 group by floor(datediff(now(), created) / 3);
https://github.com/Bantik/seer
# declare a struct to hold the resultsUserCountByDate = Struct.new(:date, :count) def report @user_counts = User.count( :group => "DATE(created_at)", :conditions => ["created_at >= ? ", 7.days.ago], :order => "DATE(created_at) ASC" ).collect do |date, count| UserCountByDate.new(date, count) endend
<div id="chart"></div><%= Seer::visualize( @user_counts, :as => :column_chart, :in_element =>'chart', :series => { :series_label => 'date', :data_method => 'count' }, :chart_options => { :height => 300, :width => 100 * @user_counts.size, :is_3_d => true, :legend => 'none', :colors => "[{color:'#990000', darker:'#660000'}]", :title => "New users in last 7 days", :title_x => 'date', :title_y => 'count' } ) -%>
在那里，有我们特有的记忆，亲情之忆、
