Question

I have a different situation that a category can be a sub category of more than one category. How should I design this ?

The tree structure below doesnt solve my problem I guess. Should I do ParentCategoryId as a string and can take multiple category id in it. Then do calculation to resolve parent categories or do you advise me another solution ? What is your optimum solution to solve this problem ?

--Category--

Id
ParentCategoryId
CategoryName

Thanks in advance,

Answer 1

The standard SQL solution for this is a cross table. You would have two tables, categories and categories_x as follows:

categories
+------------+------------+
|categoryId  |name        |
+------------+------------+
|1           |foo         |
+------------+------------+
|2           |bar         |
+------------+------------+
|3           |huh         |
+------------+------------+

categories_x
+------------+------------+
|categoryId  |parentId    |
+------------+------------+
|3           |1           |
+------------+------------+
|3           |2           |
+------------+------------+

To get the parents of category 3 your sql query would look like:

SELECT categoryId, name 
  FROM categories 
  WHERE categoryId IN (SELECT parentId FROM categories_x WHERE categoryId = 3)