Question

Not sure if mySQL allows for this, but am curious if it is.

I have a simple ACL db, there are channels and users. Some users have access to specific channels, others have access to all of them. My preferred method would not be to have a row in the permissions table for each user’s channel, but to specify that if the channel id column in a user’s row is NULL then they have access to any channel. In other words…

channels
1 | channelA
2 | channelB
etc...

users_access
1 | NULL // this user has access to all channels
2 | 2 // this user only has access to channel 2

Is there a way to write a select that returns 1 and 2 for user 1 (based on the NULL) and just 2 for user 2?

Again… I recognize that the alternative design is to simply have a unique row in the user’s table for each channel they have the rights to, but for various reasons that I don’t wish to get into, I’d prefer to have a global NULL access value.

TIA

Answer 1

SELECT 
    uc.user_id
    ch.chanell_id
FROM
    chanells AS ch
  JOIN 
    users_access AS uc
      ON uc.channel_id = ch.channel_id

UNION ALL

SELECT 
    uc.user_id
    ch.chanell_id
FROM
    chanells AS ch
  CROSS JOIN 
    users_access AS uc
WHERE uc.channel_id IS NULL  

or:

SELECT 
    uc.user_id
    ch.chanell_id
FROM
    chanells AS ch
  JOIN 
    users_access AS uc
      ON uc.channel_id = ch.channel_id
      OR uc.channel_id IS NULL 

---

You could also restructure your tables, keeping the users_access for the information about users with access to specific channels and adding a users_global_access for users with access to all channels (possibly with just one column, user_id, or with other relevant info, like start_date, etc.)