Question

To preface this question I should say I know very little about database efficiency which will become glaringly apparent very shortly.

This is a fairly simple question:

I’d like to store attendance to events within a mysql database.
I’ve thought of two possible methods (there are more, I’m sure):

1. Create an additional attendance row in the events table, containing a comma separated list of user ids
2. Create an attendance table, containing two columns, event_id and user_id

My instinct says that method 2 would be the most efficient — although multiple rows would have to be returned and traversed, this is likely less costly than searching for a particular user_id within a concatinated string…

Can anyone confirm this?

Answer 1

The second option is better. Searching in a comma separated string is time consuming.

However in the 2nd option, make sure the event_id and the user_id are FOREIGN KEYS.

This will INDEX the columns and you will have better searching results.