使用 SQL 显示子类别

Question

好吧，这有点令人困惑，所以我决定写一个新问题。

我需要检查我的类别表中的一行是否是子类别。然后我需要检查孩子属于哪个父类别？

父类别的 categoryID 和 ParentCategoryID 为 0 子类别有一个 categoryID 和一个 ParentCategoryID，例如 30。

分类表：

ID PCID NAME
10  0   Computers
11  10  Software
12  10  Hardware

这是我尝试过的：

这将显示父类别（因为 PCID 0 是父类别）：

SELECT        CategoryID, ParentCategoryID, Name, Published, Deleted, PictureID
FROM          Nop_Category
WHERE        (Deleted = 0) 
AND          (Published = 1) 
AND          (ParentCategoryID = 0)

Answer 1

自连接回表以查找孩子的实际父母。

SELECT        c1.CategoryID, c2.ParentCategoryID, c1.Name, c2.Name as ParentName, c1.Published, c1.Deleted, c1.PictureID
FROM          Nop_Category c1
JOIN          Nop_Category c2 on c1.ParentCategoryId = c2.CategoryId
WHERE        (c1.Deleted = 0)  
AND          (c1.Published = 1)  
AND          (c1.ParentCategoryID = 10)

这将返回“计算机”类别的两个子项。这就是你要找的吗？

当然，您可以反过来显示特定父级或所有父级的所有子级：

SELECT c.*, p.* -- shortened, but you should pick specific columns

FROM Nop_Category p -- parent
JOIN Nop_Category c ON c.ParentCategoryId = p.CategoryId -- children

WHERE p.ParentCategoryId = 0 -- all top level parents


SELECT c.*, p.* -- shortened, but you should pick specific columns

FROM Nop_Category p -- parent
JOIN Nop_Category c ON c.ParentCategoryId = p.CategoryId -- children

WHERE p.CategoryId = 10 -- only the "Computers" category

或者，如果您只想要“计算机”类别的孩子，请将您的 ParentCategoryId 更改为 10

SELECT        CategoryID, ParentCategoryID, Name, Published, Deleted, PictureID  
FROM          Nop_Category  
WHERE        (Deleted = 0)   
AND          (Published = 1)   
AND          (ParentCategoryID = 10)