Question

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

myshell> bash
bash-3.2$ exit
exit

实际输出：

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

预期输出：

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

样本数据库数据：

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

Answer 1

您可以使用DISTINCT关键字重复显示结果。

    SELECT GROUP_CONCAT(CONCAT_WS(',',DISTINCT 
    t1.CategoryID,DISTINCT t2.CategoryID,DISTINCT t3.`CategoryID`,DISTINCT  
    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

来自mysql查询的重复结果

1 个答案: