vlog/book-mapper/src/main/resources/mapper/CommentMapperCustom.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd" >
<mapper namespace="com.imooc.mapper.CommentMapperCustom" >

  <!--
      FIXME
      思考：阿里规范明确规定不能超过三表关联，这里达到了四张表
      我们应该如何优化呢？使得sql脚本查询表位三表或者两表查询
      来实现呢又或者说我们能不能不使用数据库，使用别的手段（中间件）？mycat
   -->
  <select id="getCommentList" parameterType="map" resultType="com.imooc.vo.CommentVO">

      SELECT
          c.id as commentId,
          c.vlog_id   as vlogId,
          u.id as vlogerId,
          u.nickname as commentUserNickname,
          u.face as commentUserFace,
          c.father_comment_id as fatherCommentId,
          c.comment_user_id as commentUserId,
          c.content as content,
          c.like_counts as likeCounts,
          fu.nickname as replyedUserNickname,
          c.create_time as createTime
      FROM
          `t_comment` as c
      LEFT JOIN
          t_users as u
      ON
          c.comment_user_id = u.id
      LEFT JOIN
          `t_comment` as fc
      ON
          c.father_comment_id = fc.id
      LEFT JOIN
          t_users as fu
      ON
          fc.comment_user_id = fu.id
      WHERE
          c.vlog_id = #{paramMap.vlogId}
      ORDER BY
          c.like_counts DESC,
          c.create_time DESC
  </select>

</mapper>