sql_select_from_group.rb

#acts-as-taggable-on-2.0.0.rc1/lib/acts_as_taggable_on/acts_as_taggable_on/related.rb [RO] 64,3 
      def related_tags_for(context, klass, options = {})
        tags_to_find = tags_on(context).collect { |t| t.name }

        exclude_self = "#{klass.table_name}.id != #{id} AND" if self.class == klass

        klass.scoped({ :select     => "#{klass.table_name}.*, COUNT(#{Tag.table_name}.id) AS count",
                 :from       => "#{klass.table_name}, #{Tag.table_name}, #{Tagging.table_name}",
                 :conditions => ["#{exclude_self} #{klass.table_name}.id = #{Tagging.table_name}.taggable_id AND #{Tagging.table_name}.taggable_type = '#{klass.to_s}' AND #{Tagging.table_name}.tag_id = #{Tag.table_name}.id AND #{Tag.table_name}.name IN (?)", tags_to_find],
                 :group      => grouped_column_names_for(klass),
                 :order      => "count DESC" }.update(options))
      end