如何在SQL表中正确使用FK

Question

Table Department :

DeptId
Name

Table Team

TeamId
*DeptId (FK)
Name

Table Employee

EmpId
*DeptId
*TeamId

I am making some updates on an old project, but I don't know why the old programmer designed those tables like this (like putting both DeptId and TeamId in the Employee table).

I find this useless because I can get the department from the Team table, and there's no need to put both FK IDs into the Employee table, TeamId is enough.

Is there any other reason that could force me to put both FKs in that table?

Thank you.

Answer 1

As the data model is written, an employee could be a member of a team that is not in his or her department.

That is probably possible, for instance, if the employee is temporarily on loan.

My bigger problem with the data model is that the relationships between employee and team and employee and department vary over time. So, I would have three tables for each entity. The only relationship in the tables would be between team and department (because that presumably does not change over time).

Then I would have two junction tables, one employeeDepartments and one employeeTeams that capture the changing relationships over time.