Question

我正在尝试获取此查询的层次结构级别。这是CTE递归查询

WITH CategoryRec AS 
(
    SELECT Id, Parentid, Name
    FROM dbo.Category

    UNION ALL

    SELECT cr.Id, c.Parentid, cr.Name
    FROM CategoryRec AS cr INNER JOIN dbo.Category AS c ON cr.Parentid = c.Id
    WHERE c.Parentid IS NOT NULL
)
SELECT DISTINCT Id, Parentid, Name
FROM  CategoryRec

此问题与此问题有关：How to get the full Hierarchy with SQL CTE

感谢您的帮助

Answer 1

您需要添加一个名为Level的列（或任何您想要调用的列） - 两者都是“锚点”SELECT以及CTE的递归部分 - 如下所示：

WITH CategoryRec AS 
(
    SELECT Id, Parentid, Name, 1 AS 'Level'
    FROM dbo.Category

    UNION ALL

    SELECT cr.Id, c.Parentid, cr.Name, cr.Level + 1 
    FROM CategoryRec AS cr 
    INNER JOIN dbo.Category AS c ON cr.Parentid = c.Id
    WHERE c.Parentid IS NOT NULL
)
SELECT DISTINCT Id, Parentid, Name, Level
FROM  CategoryRec

Answer 2

您需要在第一个查询中选择层次结构的顶级，级别为marc_s。

;WITH CategoryRec AS 
(
  SELECT a.Id, 
         a.Parentid, 
         a.Name, 
         1 AS 'Level'
    FROM dbo.Category as a
   WHERE a.Parentid IS NULL

  UNION ALL

  SELECT b.Id, 
         b.Parentid, 
         b.Name, 
         a.Level + 1 
    FROM CategoryRec  as a
           INNER JOIN 
         dbo.Category as b on b.Parentid = a.Id
   WHERE b.Parentid IS NOT NULL
)
SELECT Id, Parentid, Name, Level
FROM  CategoryRec

Answer 3

返回正确的级别。但不确定这个查询是否符合性能应该是

WITH CategoryRec AS 
(
    SELECT     Id, Parentid, Name, 1 as [Level]
    FROM dbo.Category
    where Parentid IS NULL

    UNION ALL

    SELECT c.Id, c.Parentid, c.Name, (cr.[Level] + 1) as [Level]
    FROM Category c INNER JOIN
    CategoryRec AS cr ON c.Parentid = cr.Id
),
CategoryRec2 as
(
    SELECT Id, Parentid, Name, [Level]
    FROM CategoryRec

    UNION ALL

    SELECT cr.Id, c.Parentid, cr.Name, cr.[Level]
    FROM CategoryRec2 AS cr INNER JOIN
    CategoryRec AS c ON cr.Parentid = c.Id
    WHERE c.Parentid IS NOT NULL
)
SELECT Id, Parentid, Name, [Level]
FROM CategoryRec2

如何获取此查询的层次结构级别

3 个答案: