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

Delimited String of Ancestors

If you're strongly considering the 5-level relationship table, it may simplify things to use a delimited string of ancestors instead of 5 separate columns.

user_id  depth   ancestors
10       7       9,7,4,3,2,1
9        6       7,4,3,2,1
...
2        2       1
1        1       (empty string)

Here are some SQL commands you'd use with this model:

To add user 11, referred by user 10

insert into ancestors_table (user_id, depth, ancestors)
select 11, depth+1, concat(10,',',ancestors)
from ancestors_table
where user_id=10;

To find all users referred by user 3. (Note that this query can't use an index.)

select user_id
from ancestors_table
where ancestors like '%,3,%' or ancestors like '3,%' or ancestors like '%,3';

To find the ancestors of user 10. You need to break up the string in your client program. In Ruby, the code would be ancestorscolumn.split(",").map{|x| x.to_i}. There's no good way to break up the string in SQL.

select ancestors from ancestors_table where user_id=10;

To find the number of users at each level, referred by user 3:

select
   depth-(select depth from ancestors_table where user_id=3),
   count(*)
from ancestors_table
where ancestors like '%,3,%' or ancestors like '3,%' or ancestors like '%,3'
group by depth;

You can avoid SQL injection attacks in the like '%,3,%' parts of these queries by using like concat('%,', ?, ',%') instead and binding the an integer for the user number to the placeholder.