Maintain many level hierarchy of tables in database - php

Question

I have to maintain the data of friend list of friends who liked a particular category post. And this may be at any level. For eg.
if a friend of A who is B like a wanted post. then I ll maintain the record of A’s friends and B’s friend. Basically my requirement is
If user visit my product site I have to tell him/her that you're following friend already visited the same and they actually recommend you to use this and to build confidence that you are on the right way as your friends are also using it. I also want to suggest A that C who is the friend to B is using this product since this time and C suggest to many for using it.
I know this logic is already implemented in good sites.
I am just a starter. So pls suggest me the database for backend and required things for frontend.
Specially this question is to maintain the record on database. So I am asking for the database what should I use not how should I implement that would be next step.
As I am planning to use Graph database for it. In graph either bigdata or Neo4j.
Your ideas are most welcome and will be appreciated. Thanks

Answer 1

I hope my logic may takes you few steps forward
Initially we have to maintain the mutual friends records
foe example
id mut_id
1 2,3,4
Here 2,3,4 are your friends
next we need to maintain the records who has purchased/visited
prod_id buy_id
1 2,1
Now suppose 3 id wants to buy or visit site then we can show that your friend already visited or buyed product

Answer 2

Friends' relations is a classical many-to-many scheme. You need two tables to implement this:
1. A table with personal data, such as name, email etc. (could be more complex like person-properties relation)
2. A table with friends' retaionships data, usually it contains ID pairs of friends that relation is representing and some data about relation itself, such as category (friend/family/classmate etc) , level of affinity (if >0 it means positive relation, <0 negative such as enemies) and so on. Assume first ID is a person this relation belongs to (and can be maintained by), second ID is a person this relation applies to. Usually such kind of tables is constrained to pair of IDs to be unique, so nobody will be able to add same person as a friend twice
Here is some sample:
CREATE TABLE person
(
id INT NOT NULL AUTO_INCREMENT,
name VARCHAR(255),
email VARCHAR(255),
PRIMARY KEY (person_id)
);
CREATE TABLE relationship
(
id_person INT NOT NULL REFERENCES person(id),
id_person_related INT NOT NULL REFERENCES person(id),
id_category INT REFERENCES relcategories(id),
affinity INT,
PRIMARY KEY (id_person, id_person_related)
);
Note that affinity and id_category fiels are optional and last one requires table relcategories with INT id field to be create first
Visits of one friend to another can also be stored in relationship in a separate field