Storing Hierarchical Data (MySQL) for Referral Marketing

Question

I need to have a 5 levels hierarchy for the users registered to a website. Every user is invited by another, and I need to know all descendants for a user. And also ancestor

Answer 1

Closure Table

ancestor_id  descendant_id  distance
    1            1              0
    2            2              0
    3            3              0
    4            4              0
    5            5              0
    6            6              0
    2            3              1

To add user 10, referred by user 3. (I don't think you need to lock the table between these two insertions):

insert into ancestor_table
select ancestor_id, 10, distance+1
from ancestor_table
where descendant_id=3;

insert into ancestor_table values (10,10,0);

To find all users referred by user 3.

select descendant_id from ancestor_table where ancestor_id=3;

To count those users by depth:

select distance, count(*) from ancestor_table where ancestor_id=3 group by distance;

To find the ancestors of user 10.

select ancestor_id, distance from ancestor_table where descendant_id=10;

The drawback to this method is amount of storage space this table will take.