如何为2列MySQL创建约束

Question

I have have created a database with 3 tables:
Products
Categories
Subcategories

In my products table I have a category and a subcategory column:

| product_name | category | subcategory|  
----------------------------------------    
| varchar      | int      | int        |

As of right now the category column references the categories table id and the subcategory column references the subcategories id.

The categories column has an id and a category name column:

| id | category_name |
----------------------
|int | varchar       |

The subcategories column has an id, sub category and a parent column which is a foreign key that references the categories(id) column.

| id | subcategory_name | parent |
---------------------------------
|int | varchar          | int    |

I wanted to know if there is a way to add a constraint to the products's 'subcategories' column so that one would only be able to add a value if it was a legitimate child of the parent category.

Forgive me if this question has been answered already. I do not know the proper name for what I am trying to do.

Answer 1

1 - you can use program to verify before insert / update the sub-cat id

2 - or you can use a trigger to run after each transaction

3 - or you can redesign your category and sub-category table, it depends on how your category data look.

eg:

id   category_name
---- -------------
10   cat 10
1011 kid of cat 10
20   cat 20
2020 kid of cat 20

4 - If you do not like above design, you can also design this way:

id   category      parent_id
---- ------------- -----
10   cat 10         0
1010 kid of cat 10  10
20   cat 20         0
2020 kid of cat 20  20