小编Sür*_* AK的帖子

执行查询后，尝试获取树结构类别ID时，将获得重复的ID。我们期望输出没有重复的ID

SELECT 
  GROUP_CONCAT(CONCAT_WS(',',t1.CategoryID,t2.CategoryID,t3.`CategoryID`, t4.CategoryID)) AS id 
FROM prodcategory AS t1 
LEFT JOIN prodcategory AS t2 ON t2.ParentCategoryID = t1.CategoryID 
LEFT JOIN prodcategory AS t3 ON t3.ParentCategoryID = t2.CategoryID 
LEFT JOIN prodcategory AS t4 ON t4.ParentCategoryID=t3.CategoryID 
WHERE t1.ParentCategoryID =41

实际输出：

190,256,190,257,191,261,300,191,262,192,267

预期产量：

190,256,257,191,261,300,262,192,267

样本数据库数据：

CategoryID |  CategoryName |  ParentCategoryID
   41      |       a       |        1
   190     |       b       |        41
   191     |       c       |        41
   192     |       d       |        41
   256     |       e       |        190
   257     |       f       |        190
   261     | …