mysql 子节点拼接父节点

表结构

 子节点拼接父节点希望得到结果：

sql 语句：

SELECT 
  b1.id AS 'ID',
  IF(
    b1.detail_index = '',
    CONCAT(b2.detail_index, '_', '子类'),
    IF(
      b1.parent_id = 0,
      b1.detail_index,
      CONCAT(b2.detail_index, '_', b1.detail_index)
    )
  ) AS '索引',
  b1.detail_label AS '条目名称',
  IFNULL(b1.detail_note, '') AS '条目备注' 
FROM
  system_dictionary_details_copy AS b1 
  LEFT JOIN system_dictionary_details_copy AS b2 
    ON b1.parent_id = b2.id 
WHERE 1 = 1