Question

I need to join tables to do aggregation. I suck at that. Here’s my scenario:

CATEGORIES
CatID | CategoryName | Parent
1     | Cars         | NULL
2     | Electronics  | NULL
3     | DVD          | 2
4     | Blu_ray      | 2
5     | Shoes        | NULL

So basically, topmost elements don’t have parents. Then I have

PRODUCTS
ProdID | Prod Name        | CatID
1      | DVD Player 1     | 3
2      | Blu-Ray Player   | 3
3      | Nike             | 5
4      | DVD Player 2     | 3

I want to end up with…

CATEGORIES
CatID | CategoryName | Parent | totalProds
1     | Cars         | NULL   | 0
2     | Electronics  | NULL   | 0
3     | DVD          | 2      | 2
4     | Blu_ray      | 2      | 1
5     | Shoes        | NULL   | 1

Any ideas?

Answer 1

Aren’t you just asking for the total number of products per category?

SELECT CatID, CategoryName, Parent, COUNT(*) totalProds
FROM categories c
INNER JOIN products p ON p.CatID = c.CatID
GROUP BY CatId