Solved

Relational Algebra expression am I correct?

Posted on 2011-09-11
9
372 Views
Last Modified: 2012-05-12
Provide an expression in relational algebra that shows the following query:
Find the names, genders and social security numbers of all employees who have been managers in the last 2 years.

    * employee (emp_id,f_name,l_name,dob,ssn,gender,hire_date)
    * address (emp_id,street,city,state,zip,country,phone)
    * department (dept_id,name)
    * emp_in_dept (emp_id,dept_id,begin_date,end_date)
    * mgr_of_dept (dept_id,emp_id,begin_date,end_date)
    * salary(emp_id,salary,begin_date,end_date)
    * job_title(emp_id,title,begin_date,end_date)

I started with this but I am not sure how to complete the comparing part.

PROJECT f_name, l_name, gender, ssn, (
0
Comment
Question by:Rowley4
  • 5
  • 3
9 Comments
 
LVL 59

Expert Comment

by:Kevin Cross
ID: 36519350
Rowley4, is this a school assignment? Not a big deal if it is, we just need to ensure we are "teaching" you correctly if it is. :)

With that in mind, please post what you have tried so far. It appears it got cut off. With your code as a starting point, we can help guide you.
0
 

Author Comment

by:Rowley4
ID: 36519364
I have started the code, but I am unsure how to finish it. This is what I have so far.

PROJECT f_name, l_name, gender, ssn, (

I am jut not sure how to write the comparing part when I have no actual dates. I thought it would be > 2009? But not sure how to put that in.
0
 

Author Comment

by:Rowley4
ID: 36519375
This is separate from my other question.
0
 
LVL 59

Expert Comment

by:Kevin Cross
ID: 36519407
What you have there isn't close to a SQL statement, so not sure what to put next either. so this homework. I will see what I can mock up to help explain things for you like Patrick did in your other question.
0
Is Your Active Directory as Secure as You Think?

More than 75% of all records are compromised because of the loss or theft of a privileged credential. Experts have been exploring Active Directory infrastructure to identify key threats and establish best practices for keeping data safe. Attend this month’s webinar to learn more.

 

Author Comment

by:Rowley4
ID: 36519410
I am using Relational Algebra for this one rather than just SQL.
0
 
LVL 59

Accepted Solution

by:
Kevin Cross earned 500 total points
ID: 36519461
See if this helps get you going: http://db.grussell.org/section010.html#_Toc67114473
Something like this:
PROJECT f_name, l_name, gender, ssn (SELECT begin_date >= '20090101' (employee JOIN employee.emp_id = mgr_of_dept.emp_id mgr_of_dept))

Assumptions: employee managed a department; could have a manager in title only, which you could capture by making the relationship to job_title. Hopefully this helps you get going. You can combine the PROJECT and SELECT for what you need.
0
 

Author Comment

by:Rowley4
ID: 36519466
Yes!! Perfect.. This was a great.
0
 

Author Closing Comment

by:Rowley4
ID: 36519467
This is exactly what I needed. Thank you so much!
0

Featured Post

Is Your Active Directory as Secure as You Think?

More than 75% of all records are compromised because of the loss or theft of a privileged credential. Experts have been exploring Active Directory infrastructure to identify key threats and establish best practices for keeping data safe. Attend this month’s webinar to learn more.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

A Guide to the PMT, FV, IPMT and PPMT Functions In MS Excel we have the PMT, FV, IPMT and PPMT functions, which do a fantastic job for interest rate calculations.  But what if you don't have Excel ? This article is for programmers looking to re…
Introduction On a scale of 1 to 10, how would you rate our Product? Many of us have answered that question time and time again. But only a few of us have had the pleasure of receiving a stack of the filled out surveys and being asked to do somethi…
Hi friends,  in this video  I'll show you how new windows 10 user can learn the using of windows 10. Thank you.
This is a video describing the growing solar energy use in Utah. This is a topic that greatly interests me and so I decided to produce a video about it.

912 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question

Need Help in Real-Time?

Connect with top rated Experts

17 Experts available now in Live!

Get 1:1 Help Now