to set foreign key or not to set?

[jrahma]

Hi,

I want to ask about indexing.

I have employee table and department table with employee_id and department_id primary keys. Also I have department_id in the employee table.

Do I set the employee.department_id as a foreign key for a better performance?

Thanks,
Jassim

[laserlight]

It sounds like it is a foreign key by design. So, why not declare it so?

[jrahma]

i indexed the field but do I still need to declare it as foreign key?

[traq]

A foreign key is not simply an index. It defines a relationship between to tables. It sounds like there is such a relationship, so, yes: make it a foreign key.

This isn't about efficiency, though, it's about the integrity of your data and its structure.