Question

我的表格包含以下数据：

CategoryId  CategoryName    ParentCategoryId
1             abc                       null
2             abc1                      1
3             abc2                      1
4             def                       null
5             def1                      4
6             def2                      4
7             ghi                       null
8             ghi1                      7
9             ghi2                      7

我使用以下查询在此表上使用了自联接：

select p.CategoryId as ParentCategoryId, p.CategoryName as ParentCategoryName,
       c.CategoryId as CategoryId, c.CategoryName as CategoryName 
from Categories c, Categories p
where c.ParentCategoryId = p.CategoryId

此查询为每个categoryid生成父类别ID和名称的重复行。

我希望PraentCategoryId出现在所有相应子类别中一次。

我还需要做些什么，或者有办法修改此查询。

上述查询的结果就像

ParentCategoryId    ParentCategoryName  CategoryId  CategoryName
    1             abc                       2        abc1
    1             abc                       3        abc2
    4             def                       5        def1
    4             def                       6        def2
    7             ghi                       8        ghi1
    7             ghi                       9        ghi2

Answer 1

我使用JOIN放置了两个版本的查询。第一个将显示每个父项，每个子项都在自己的行上。第二个使用GROUP_CONCAT将子类别放在逗号分隔的列表中，每个父类别一行。

select 
    p.CategoryId as ParentCategoryId, 
    p.CategoryName as ParentCategoryName,
    c.CategoryId as CategoryId, 
    c.CategoryName as CategoryName 
from Categories c
JOIN Categories p
ON c.ParentCategoryId = p.CategoryId

select 
    p.CategoryId as ParentCategoryId, 
    p.CategoryName as ParentCategoryName,
    GROUP_CONCAT(c.CategoryId) as CategoryIds, 
    GROUP_CONCAT(c.CategoryName) as CategoryNames
from Categories c
JOIN Categories p
ON c.ParentCategoryId = p.CategoryId
GROUP BY p.`CategoryId`
ORDER BY p.`CategoryId`

第二个查询的输出：

ParentCategoryId    |   ParentCategoryName  |   CategoryIds |   CategoryNames
1   |   abc |   2,3 |   abc1,abc2
4   |   def |   5,6 |   def1,def2
7   |   ghi |   9,8 |   ghi2,ghi1

Answer 2

希望这可以解决您的问题，

;WITH cte 
     AS (SELECT p.categoryid   AS ParentCategoryId, 
                p.categoryname AS ParentCategoryName, 
                c.categoryid   AS CategoryId, 
                c.categoryname AS CategoryName 
         FROM   Categories  c 
                JOIN Categories  p 
                  ON c.parentcategoryid = p.categoryid) 
SELECT DISTINCT ParentCategoryId, 
                ParentCategoryName, 
                Stuff((SELECT ',' + Cast(t1.categoryid AS VARCHAR(10)) 
                       FROM   cte t1 
                       WHERE  t.parentcategoryid = t1.parentcategoryid 
                       FOR xml path('')), 1, 1, '') AS CategoryId, 
                Stuff((SELECT ',' + t2.categoryname 
                       FROM   cte t2 
                       WHERE  t.parentcategoryid = t2.parentcategoryid 
                       FOR xml path('')), 1, 1, '') AS CategoryName 
FROM   cte t

单个出现的父母ID＆＃39;在自我加入

2 个答案: