Question

My system uses a table of users with several elements including their online status. Now I would like to add a feature so each user can add a contact i.e an existing user from the database into their list of friends or contacts showing their name and online status. However I need any changes in the online status to updated on the contact list as they happen so creating a new table wouldn’t help.

I have been looking into views for this but don’t have too much experience with databases to I would like to know if this is the correct way of going about it and a bit more detail on how to do it.

Here are the steps I was thinking of:

1. When users registers, create a view i.e view_name = username_view.
2. To add a contact select data from main users table and add to user’s view
3. To delete a contact delete selected data from view.

I am not sure if this is possible with views so if it isn’t can some please help me out.

Thanks.

Answer 1

ER databases = Entites and Relations databases handle that by have one table whit the entites “users”, and one table for the relationship “friends” that connect a user to another user.

a query for that can be:

SELECT users.* 
FROM friends 
LEFT JOIN users ON (users.user_id = friends.friend_id) 
WHERE friends.user_id = :user

Exemple:

a user table, for the entity user

CREATE TABLE user (user_id SERIAL, name TINYTEXT NOT NULL);

exemple users

user_id | name
      1 | Anna
      2 | Bertil
      3 | Carl
      4 | David
      5 | Erik

a friends tabel, for relations between two users, (not one per user, just one)

CREATE TABLE friends (
  user_id BIGINT UNSIGNED NOT NULL,
  friend_id BIGINT UNSIGNED NOT NULL,
  PRIMARY KEY (user_id, friend_id)
);

if Anna adds Beril and Carl as friends, and Carl adds David and Erik as friends, the content of the table going to be:

user_id | friend_id
      1 |         2
      1 |         3
      3 |         4
      3 |         5

if we want to list the names of Annas friends, and we allredy know that Annas user_id = 1, then we can use this query (like the one above)

SELECT users.name 
FROM friends 
LEFT JOIN users ON (users.user_id = friends.friend_id) 
WHERE friends.user_id = 1