Counting number of children in hierarchical SQL data
- by moontear
for a simple data structure such as so:
ID parentID Text Price
1 Root
2 1 Flowers
3 1 Electro
4 2 Rose 10
5 2 Violet 5
6 4 Red Rose 12
7 3 Television 100
8 3 Radio 70
9 8 Webradio 90
For reference, the hierarchy tree looks like this:
ID Text Price
1 Root
|2 Flowers
|-4 Rose 10
| |-6 Red Rose 12
|-5 Violet 5
|3 Electro
|-7 Television 100
|-8 Radio 70
|-9 Webradio 90
I'd like to count the number of children per level. So I would get a new column "NoOfChildren" like so:
ID parentID Text Price NoOfChildren
1 Root 8
2 1 Flowers 3
3 1 Electro 3
4 2 Rose 10 1
5 2 Violet 5 0
6 4 Red Rose 12 0
7 3 Television 100 0
8 3 Radio 70 1
9 8 Webradio 90 0
I read a few things about hierarchical data, but I somehow get stuck on the multiple inner joins on the parentIDs. Maybe someone could help me out here.
moon
