Share users of an existing site

Question

I have 3 q2a sites.

a.domain.com, b.domain.com, c.domain.com

These 3 sites also have a lot of users and thousands of content. I set up these three sites as normal.

When I first set up these sites, I didn't set up common user settings.

Can I merge users of these 3 sites now?

For example:

Can existing users of a.domain.com log in to c.domain.com?

Can QA_MYSQL_USERS_PREFIX be activated only on the first installer? Can it be subsequently activated in a previously installed db?

Comments

Maybe you can make a new database just for users,and from the host change the direction of database to the new "just for the users file"
I believe you should contacting with programmer to solve it.

Answer 1

TL;DR: you won't be able to achieve this now.

Long explanation is that QA_MYSQL_USERS_PREFIX just changes the prefix of the ^users table. So you can change it whenever you want. The problem is that if you already have users in a table and you stop using it... well... users will be gone.

You might think about migrating them but that's not as simple as it sounds. If you re-insert the users, then the user IDs will be different now. If you just force the user IDs to be the same, you will realize that many of them will be triplicated (e.g.: user ID 1, which is usually the super admin).

So you should first update all single user IDs to a user ID that is unique to all three sites and also update all references to it, and this is not something with the complexity of just adding/removing a prefix. Then reinsert all records keeping the original ID. So I'd recommend to leave things the way they are now unless you know what you're doing.