Solved

Relational Algebra expression am I correct?

Posted on 2011-09-11
9
391 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
Free Tool: Postgres Monitoring System

A PHP and Perl based system to collect and display usage statistics from PostgreSQL databases.

One of a set of tools we are providing to everyone as a way of saying thank you for being a part of the community.

 
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
 

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

Free Tool: Port Scanner

Check which ports are open to the outside world. Helps make sure that your firewall rules are working as intended.

One of a set of tools we are providing to everyone as a way of saying thank you for being a part of the community.

Question has a verified solution.

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

Suggested Solutions

Title # Comments Views Activity
Simplify expression 3 106
Math question 3 97
Normalised finishing position 2 48
How many living descendants from a 23 years old in 1838? 7 55
Complex Numbers are funny things.  Many people have a basic understanding of them, some a more advanced.  The confusion usually arises when that pesky i (or j for Electrical Engineers) appears and understanding the meaning of a square root of a nega…
This article seeks to propel the full implementation of geothermal power plants in Mexico as a renewable energy source.
Finds all prime numbers in a range requested and places them in a public primes() array. I've demostrated a template size of 30 (2 * 3 * 5) but larger templates can be built such 210  (2 * 3 * 5 * 7) or 2310  (2 * 3 * 5 * 7 * 11). The larger templa…
I've attached the XLSM Excel spreadsheet I used in the video and also text files containing the macros used below. https://filedb.experts-exchange.com/incoming/2017/03_w12/1151775/Permutations.txt https://filedb.experts-exchange.com/incoming/201…

808 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