按时间段分组

PostgreSQL：

<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'      }    ) -%>