Is it good database design to have admin users in the same table as front-end users?

Roles should be tracked separately from user accounts, because someone can be promoted (or demoted) over time. Would it make sense in that situation to have two different user accounts, in two different tables? I think not.

Here's the basic structure I'd use -

USERS

• user_id (primary key)
• user_name

ROLES

• role_id (primary key)
• role_name

USER_ROLES

• user_id (primary key, foreign key to USERS.user_id)
• role_id (primary key, foreign key to ROLES.role_id)

Yes, all users belong in the users table. You also need to have a Roles table and have a FK betweent the two.

The risk one a user accidentally becoming an administrative user shouldn't be bigger than a user accidentally becoming a different user, and that should definitely not happen either.

Consider that if you have regular users and administrative users in separate tables, you would have a user id in the regular user table matching a user id in the administrative user table. You would have to make sure that one type of user id could never be accidentally used as the other type. It's harder to spot a problem like that, than spotting something that could cause a user id changing into a different user id.