在层次结构中查找类别级别

Question

我有一个脚本来查找类别列表的层次结构。但是，我需要知道关卡的深度才能找到所有相应的类别。所以我的问题是有没有更好的方法来重写代码，以便它可以深入到最低级别，而无需我指定深度。如下面的示例，我必须知道类别级别达到 5 级深度才能找到所有类别。

WITH rCTE AS
(
    SELECT
        *,
        0 AS Level
    FROM dbo.inv_category ic
    WHERE ic.Primary_org_id = 56392

    UNION ALL

    SELECT
        t.*,
        r.Level + 1 AS Level
    FROM dbo.inv_category t
    INNER JOIN rCTE r ON t.Parent_id = r.Category_id
)
SELECT DISTINCT
    c1.Parent_id, c1.Category_id, c1.Category,
    c2.Category, c2.Category_id, c2.Parent_id,
    c3.Category, c3.Category_id, c3.Parent_id,
    c4.Category, c4.Category_id, c4.Parent_id,
    c5.Category, c5.Category_id, c5.Parent_id
FROM 
    rCTE c1
LEFT OUTER JOIN 
    rCTE c2 ON c1.Category_id = c2.Parent_id
LEFT OUTER JOIN 
    rCTE c3 ON c2.Category_id = c3.Parent_id
LEFT OUTER JOIN 
    rCTE c4 ON c3.Category_id = c4.Parent_id
LEFT OUTER JOIN 
    rCTE c5 ON c4.Category_id = c5.Parent_id
WHERE 
    c1.Parent_id = 0
ORDER BY 
    c1.Category, c2.Category

Answer 1

您的问题是您希望将父类别放在不同的列中，这使任务变得更加复杂。

缩短查询并避免多次连接的一个选项使用条件聚合：

with rcte as (...)
select
    max(case when level = 0 then parent_id   end) parent_id_0,
    max(case when level = 0 then category_id end) category_id_0,
    max(case when level = 0 then category    end) category_0,
    max(case when level = 1 then parent_id   end) parent_id_1,
    max(case when level = 1 then category_id end) category_id_1,
    max(case when level = 1 then category    end) category_1,   
    ...
from rcte

您可以添加更多三元组条件表达式来管理所需的最大级别；当产品的实际层次结构耗尽时，以下列将为空。

另一个选项是字符串聚合。这会为每个原始列生成一个唯一列，所有值按照它们在层次结构中出现的顺序连接：

with rcte as (...)
select
    string_agg(parent_id,      ' > ') within group(order by level) parent_ids,
    string_agg(category_id_id, ' > ') within group(order by level) category_ids,
    string_agg(category,       ' > ') within group(order by level) categories
from rcte