Question

The title might be worded strange, but it’s probably because I don’t even know if I’m asking the right question.

So essentially what I’m trying to build is a “breadcrumbish” categoricalization type system (like a file directory) where each node has a parent (except for root) and each node can contain either data or another node. This will be used for organizing email addresses in a database. I have a system right now where you can create a “group” and add email addresses to that group, but it would be very nice to add an organizational system to it.

This (in my head) is in a tree format, but I don’t know what tree.

The issue I’m having is building it using MySQL. It’s easy to traverse trees that are in memory, but on database, it’s a bit trickier.

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Image of tree: http://j.imagehost.org/0917/asdf.png

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SELECT * FROM Businesses:
Tim’s Hardware Store, 7-11, Kwik-E-Mart, Cub Foods, Bob’s Grocery Store, CONGLOM-O

SELECT * FROM Grocery Stores:
Cub Foods, Bob’s Grocery Store, CONGLOM-O

SELECT * FROM Big Grocery Stores:
CONGLOM-O

SELECT * FROM Churches:
St. Peter’s Church, St. John’s Church

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I think this should be enough information so I can accurately describe what my goal is.

Answer 1

Well, there are a few patterns you could use. Which one is right depends on your needs.

Do you need to select a node and all its children? If so, then a Nested set Model (Scroll down to the heading) may be better for you. The table would look like this:

| Name     | Left | Right |
| Emails   | 1    | 12    |
| Business | 2    | 7     |
| Tim's    | 3    | 4     |
| 7-11     | 5    | 6     |
| Churches | 8    | 11    |
| St. Pete | 9    | 10    |

So then, to find anything below a node, just do

SELECT name FROM nodes WHERE Left > *yourleftnode* AND Right < *yourrightnode*

To find everything above the node:

SELECT name FROM nodes WHERE Left < *yourleftnode* AND Right > *yourrightnode*

If you only want to query for a specific level, you could do an Adjacency List Model (Scoll down to the heading):

| Id | Name     | Parent_Id |
| 1  | Email    | null      |
| 2  | Business | 1         |
| 3  | Tim's    | 2         |

To find everything on the same level, just do:

SELECT name FROM nodes WHERE parent_id = *yourparentnode*

Of course, there’s nothing stopping you from doing a hybrid approach which will let you query however you’d like for the query at hand

| Id | Name     | Parent_Id | Left | Right | Path             |
| 1  | Email    | null      | 1    | 6     | /                |
| 2  | Business | 1         | 2    | 5     | /Email/          |
| 3  | Tim's    | 2         | 3    | 4     | /Email/Business/ |

Really, it’s just a matter of your needs…