See this scenario
Table: "user" - Columns: id (primary key/unsigned int), email (unique/varchar), name(varchar)
Now we also have a "order" table and two options of foreign key:
- Foreign key order.user_email + user.email
- Foreign key order.user_id + user.id
If we choose the first options instead of the second, are we going to have a negative performance impact (because the type of columns involved in the foreign key)?