Question

How can I relate a table with multiple records from another table?

Basically, I have a table for an ‘event’, how do I keep track of which ‘users’ (in their own seperate table) are in a particular event? Right now I just have a column in the ‘event’ table with a comma separated list of the users IDs who have joined that ‘event’.

There must be a better way to do this…right?

Answer 1

Typically you have a table called users_in_event which holds one row for each user in a many-to-many relationship with the events table. So for each event, you will have a number of table rows mapped individually to users.

CREATE TABLE users_in_event
( 
  user_id INT,
  event_id INT,
  FOREIGN KEY user_id REFERENCES users (user_id) ON UPDATE CASCADE,       
  FOREIGN KEY event_id REFERENCES events (event_id) ON UPDATE CASCADE
  -- Optionally, use ON DELETE CASCADE for the events foreign key
  -- FOREIGN KEY event_id REFERENCES events (event_id) ON UPDATE CASCADE ON DELETE CASCADE
)

To find out which users are in an event, do:

SELECT 
  users_in_event.user_id,
  users.name
FROM users JOIN users_in_event ON users.user_id = users_in_event.user_id
WHERE event_id=1234;