如何优化具有复杂SQL的paginate_by_sql，在查询结束时有很多 LEFT JOIN 和 GROUP BY ？

除了 paginate_by_sql ，我还有其他选择吗？

我们的项目使用Rails 2.3和Ruby 1.8和MySQL .

SELECT Table.name as sql_course_name,Table.id as sql_course_id, 
            table1.name as sql_subject_name, table1.id as sql_subject_id, 
            table3.id as sql_s_c_id, table5.*
       FROM table5
  LEFT JOIN table2 on table2.deleted = false and table2.content_id = table5.id
  LEFT JOIN lessons on lessons.deleted = false and lessons.id = table2.lesson_id
  LEFT JOIN table3 on table3.deleted = false and table3.content_id = table5.id 
  LEFT JOIN table1 on table1.deleted = false and table1.id = table3.subject_id 
  LEFT JOIN Table on Table.deleted = false and table1.course_id = Table.id
  LEFT JOIN table4 on table4.deleted = false and table4.content_id = table5.id
  LEFT JOIN attachments on attachments.deleted = false and attachments.id = table4.attachment_id
      WHERE #{str} 
   GROUP BY table5.id, table3.id
mysql sql ruby-on-rails