Question

I am creating a table for comments and one of the fields is user_id. Well both a regular user and an administrator will be able to post a comment so I’m not sure how I would do that.

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Users table has a primary key of user_id

Admins table has a primary key of admin_id

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So how would I do that?

Answer 1

If you can redesign to have a single table (login?) with an isAdmin flag, I’d do that.

If you can’t, then have a process that causes every entry in the admin table to create a related entry in the user table. The admin table can then have a user_id field to relate the two together.

In this way every admin has a user, and all comments can be made using that user_id.

I would strongly avoid having comments keyed against both user_id and admin_id, with one of them being kept NULL. It will make queries untidy, obstruct you from enforcing constraints, and tie you to he messy two-key method if you encounter a similar need anywhere else.