Question

I would like to create the following hierarchy in a sql db. This is what I have. Is it correct or is there an easier way. Also how do I query it to show the same hierarchy?

Services
    Property
        Residential
            To let
                Purchase
                Accommodation
                Maintenance
                Plumbers
                Electricians
                Carpenters
       Industrial
    To let
                 Purchase
                 Accommodation
                 Maintenance
                 Plumbers
                 Electricians
                 Carpenters

Table CategoryType

CategoryTypeID CategoryName
1   Services
2   Products
3   Main
4   MainSub
5   Sub
6   Sub1

Table Category

CateogryID      CategoryName   CategoryTypeID  ParentID
1       Property    Service
2       Residential Main        1
3        To let     MainSub 2
4       Purchase    Sub     3
5       Accommodation Sub       4

Answer 1

Your schema may work, but RDBMSs are notoriously difficult to work with when attempting to represent hierarchical data. You’ll either have a very hard time updating the table, or it will be incredibly inefficient to query against it. My suggestion if you’re going to be using such data is to consider a nested set model.

http://en.wikipedia.org/wiki/Nested_set_model

http://www.evanpetersen.com/item/nested-sets.html

There’s a bit of a learning curve, but it’s worth it.

Cheers