Relational Algebra

From: Jenski182 <jenski182_at_aol.comnojunk>
Date: 19 May 2004 22:01:22 GMT
Message-ID: <20040519180122.13396.00000914_at_mb-m06.aol.com>

I thought I got my head round relational algebra until this question came

up....

We have a database with the following relations: Division([divono],div_name,)
Department([deptno],dname,location, divno*) Employee([empno],ename,job,hiredate,sal,deptno*)

*= forgeign key
[] = primary key

what is this query doing??

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 Received on Thu May 20 2004 - 00:01:22 CEST