Re: Relational Algebra

> Project Employee over deptno giving T1
> Project Department over deptno giving T2
> T2-T1 giving T3
> Join T3, Department over deptno giving T4
> Project T4 over dname giving result
>
>
> display deptno in employee table
> display deptno in department table
> any info that is in T2 and not T1 gives T3
> Join T3? Isnt this joining onto whats already there?
> Now I'm confused.....help...
>
> Jen

T3 is department numbers that have no employees. The join brings the name of each department into the result.

(Department over { DeptNo }) minus (Employee over { DeptNo })   join Department
  over { Name };

Hope this helps Received on Thu May 20 2004 - 07:46:28 CEST