Project 1 SQL Views and Functions




Please make sure you have submitted all the questions before:


Fri 20 Apr, 5:00 pm



1. Aims


This project aims to give you practice in


• reading and understanding a moderately large relational schema (MyMyUNSW)

• implementing SQL queries and views to satisfy requests for information

• implementing SQL functions to aid in satisfying requests for information


The goal is to build some useful data access operations on the MyMyUNSW database. A theme of this project is "dirty data". As I was building the database, using a collection of reports from UNSW's information systems and the database for the academic proposal system (MAPPS), I discovered that there were some inconsistencies in parts of the data (e.g. duplicate entries in the table for UNSW buildings, or students who were mentioned in the student data, but had no enrolment records, and, worse, enrolment records with marks and grades for students who did not exist in the student data). I removed most of these problems as I discovered them, but no doubt missed some. Some of the exercises below aim to uncover such anomalies; please explore the database and let me know if you find other anomalies.


2. How to do this project:


• read this specification carefully and completely

• familiarize yourself with the database schema (description, SQL schema, summary)

• make a private directory for this project, and put a copy of the proj1.sql template there

• you must use the create statements in proj1.sql when defining your solutions

• look at the expected outputs in the expected_qX tables loaded as part of the check.sql file

• solve each of the problems below, and put your completed solutions into proj1.sql


• check that your solution is correct by verifying against the example outputs and by using the check_qX() functions


• test that your proj1.sql file will load without error into a database containing just the original MyMyUNSW data


• double-check that your proj1.sql file loads in a single pass into a database containing just the original MyMyUNSW data

• submit the project via give.


3. Introduction


All Universities require a significant information infrastructure in order to manage their affairs. This typically involves a large commercial DBMS installation. UNSW's student information system sits behind the MyUNSW web site. MyUNSW provides an interface to a PeopleSoft enterprise management system with an underlying Oracle database. This back-end system (Peoplesoft/Oracle) is often called NSS.




UNSW has spent a considerable amount of money ($80M+) on the MyUNSW/NSS system, and it handles much of the educational administration plausibly well. Most people gripe about the quality of the MyUNSW interface, but the system does allow you to carry out most basic enrolment tasks online.


Despite its successes, however, MyUNSW/NSS still has a number of deficiencies, including:


• no waiting lists for course or class enrolment

• no representation for degree program structures

• poor integration with the UNSW Online Handbook


The first point is inconvenient, since it means that enrolment into a full course or class becomes a sequence of trial-and-error attempts, hoping that somebody has dropped out just before you attempt to enrol and that no-one else has grabbed the available spot.


The second point prevents MyUNSW/NSS from being used for three important operations that would be extremely helpful to students in managing their enrolment:


• finding out how far they have progressed through their degree program, and what remains to be completed


• checking what are their enrolment options for next semester (e.g. get a list of suggested courses)


• determining when they have completed all of the requirements of their degree program and are eligible to graduate


NSS contains data about student, courses, classes, pre-requisites, quotas, etc. but does not contain any representation of UNSW's degree program structures. Without such information in the NSS database, it is not possible to do any of the above three. So, in 2007 the COMP9311 class devised a data model that could represent program requirements and rules for UNSW degrees. This was built on top of an existing schema that represented all of the core NSS data (students, staff, courses, classes, etc.). The enhanced data model was named the MyMyUNSW schema.


The MyMyUNSW database includes information that encompasses the functionality of NSS, the UNSW Online Handbook, and the CATS (room allocation) database. The MyMyUNSW data model, schema and database are described in a separate document.


4. Setting Up


To install the MyMyUNSW database under your Grieg server, simply run the following two commands:



$ createdb proj1
$ psql proj1 -f /home/cs9311/web/18s1/proj/proj1/mymyunsw.dump


If you've already set up PLpgSQL in your template1 database, you will get one error message as the database starts to load:


psql:mymyunsw.dump:NN: ERROR: language "plpgsql" already exists




You can ignore this error message, but any other occurrence of ERROR during the load needs to be investigated.


If everything proceeds correctly, the load output should look something like:


SET

SET

SET

SET

SET

psql:mymyunsw.dump:NN: ERROR: language "plpgsql" already exists

… if PLpgSQL is not already defined,

… the above ERROR will be replaced by CREATE LANGUAGE


SET

SET

SET

CREATE TABLE

CREATE TABLE

… a whole bunch of these

CREATE TABLE

ALTER TABLE

ALTER TABLE

… a whole bunch of these

ALTER TABLE


Apart from possible messages relating to plpgsql, you should get no error messages. The database loading should take less than 60 seconds on Grieg, assuming that Grieg is not under heavy load. (If you leave your project until the last minute, loading the database on Grieg will be considerably slower, thus delaying your work even more. The solution: at least load the database Right Now, even if you don't start using it for a while.) (Note that the mymyunsw.dump file is 50MB in size; copying it under your home directory or your /srvr directory is not a good idea).


If you have other large databases under your PostgreSQL server on Grieg or you have large files under your /srvr/YOU/ directory, it is possible that you will exhaust your Grieg disk quota. In particular, you will not be able to store two copies of the MyMyUNSW database under your Grieg server. The solution: remove any existing databases before loading your MyMyUNSW database.


If you are running PostgreSQL at home, the file proj1.tar.gz contains copies of the files: mymyunsw.dump, proj1.sql to get you started. You can grab the check.sql separately, once it becomes available. If you copy proj1.tar.gz to your home computer, extract it, and perform commands analogous to the above, you should have a copy of the MyMyUNSW database that you can use at home to do this project.


A useful thing to do initially is to get a feeling for what data is actually there. This may help you understand the schema better, and will make the descriptions of the exercises easier to understand. Look at the schema. Ask some queries. Do it now.


Examples …


$ psql proj1



… PostgreSQL welcome stuff …


proj1=# \d

… look at the schema …

proj1=# select * from Students;

… look at the Students table …

proj1=# select p.unswid,p.name from People p join Students s on (p.id=s.id);

… look at the names and UNSW ids of all students …

proj1=# select p.unswid,p.name,s.phone from People p join Staff s on (p.id=s.id);

… look at the names, staff ids, and phone #s of all staff …

proj1=# select count(*) from Course_Enrolments;

… how many course enrolment records …

proj1=# select * from dbpop();

… how many records in all tables …


proj1=# select * from transcript(3197893);

… transcript for student with ID 3197893 …

proj1=# … etc. etc. etc.

proj1=# \q


You will find that some tables (e.g. Books, Requirements, etc.) are currently unpopulated; their contents are not needed for this project. You will also find that there are a number of views and functions defined in the database (e.g. dbpop() and transcript() from above), which may or may not be useful in this project.


Summary on Getting Started


To set up your database for this project, run the following commands in the order supplied:

$ createdb proj1


$ psql proj1 -f /home/cs9311/web/18s1/proj/proj1/mymyunsw.dump $ psql proj1


… run some checks to make sure the database is ok $ mkdir Project1Directory

… make a working directory for Project 1


$ cp /home/cs9311/web/18s1/proj/proj1/proj1.sql Project1Directory


The only error messages produced by these commands should be those noted above. If you omit any of the steps, then things will not work as planned.


Notes


Read these before you start on the exercises:


• the marks reflect the relative difficulty/length of each question

• use the supplied proj1.sql template file for your work


• you may define as many additional functions and views as you need, provided that (a) the definitions in proj1.sql are preserved, (b) you follow the requirements in each question on what you are allowed to define


• make sure that your queries would work on any instance of the MyMyUNSW schema; don't customize them to work just on this database; we may test them on a different database instance




• do not assume that any query will return just a single result; even if it phrased as "most" or "biggest", there may be two or more equally "big" instances in the database


• you are not allowed to use limit in answering any of the queries in this project


• when queries ask for people's names, use the Person.name field; it's there precisely to produce displayable names


• when queries ask for student ID, use the People.unswid field; the People.id field is an internal numeric key and of no interest to anyone outside the database


• unless specifically mentioned in the exercise, the order of tuples in the result does not matter; it can always be adjusted using order by. In fact, our check.sql will order your results automatically for comparison.


• the precise formatting of fields within a result tuple does matter; e.g. if you convert a number to a string using to_char it may no longer match a numeric field containing the same value, even though the two fields may look similar


• develop queries in stages; make sure that any sub-queries or sub-joins that you're using actually work correctly before using them in the query for the final view/function

• You can define either SQL views OR SQL functions to answer the following questions.


• If you meet with error saying something like “cannot change name of view column”, you can drop the view you just created by using command “drop view VIEWNAME cascade;” then create your new view again.


Each question is presented with a brief description of what's required. If you want the full details of the expected output, take a look at the expected_qX tables supplied in the checking script.


5. Tasks


To facilitate the semi-auto marking, please pack all your SQL solutions into view or function as defined in each problem (see details from the solution template we provided).


Q1 (2 marks)


Define an SQL view Q1(unswid,name) that gives the student id and name of any international student who has got at least 85 marks in more than 20 courses. The name should be taken from the People.name field for the student, and the student id should be taken from People.unswid field.



Q2 (2 marks)


Define a SQL view Q2(unswid,name) that displays unswid and name of all the rooms in Computer Science Building whose types are Meeting Room and capacity are no less than 20. The view should return the following details about each room:


• unswid should be taken from Rooms.unswid field.


• name should be taken from Rooms.longname field.


• Since there are dirty data in the database, ignore rooms whose capacity is null.



Q3 (2 marks)


Define a SQL view Q3(unswid,name) that displays unswid and name of all the staff who teached student Stefan Bilek. The view should return the following details about each staff:


• unswid should be taken from People.unswid field.



• name should be taken from People.name field.




Q4 (2 marks)


Define a SQL view Q4(unswid,name) that gives all the students who enrolled in COMP3331 but not in COMP3231 (COMP3331 and COMP3231 refer to the Subjects.code). The view should return the following details about each student:

• unswid should be taken from People.unswid field.


• name should be taken from People.name field.


Note: Keep duplicate records or remove duplicate records are both correct for this question.


Q5 (2 marks)

Define SQL views Q5a(num), Q5b(num), which give the number of, respectively

l local students enrolled in 11S1 in stream(s) named Chemistry


l international students enrolled in 11S1 in degrees offered by School of Computer Science and Engineering


Note: Do not count duplicate records for this question.


Q6 (2 marks)


Write a SQL function that takes a UNSW course code as parameter and returns course name and units of credit (UOC) in the format of code (use the code field from the Subjects table), name (use the name field from the Subjects table) and UOC (use the uoc field from the Subjects table) concatenated (e.g., ‘COMP9311 Database Systems 6’). The function should be defined as follows:


create or replace function Q6(text) returns text Note that there is a space between code, name and UOC.



Note: If there is more than one subject with the same code, return one of them.


Q7 (3 marks)


Define a SQL view Q7(code,name) that displays all the programs which have more than 50 percent of international students. In a program, the percent of international students is defined as the number of international students / the number of all the students. The view should return the following details about each program:


• code should be taken from Programs.code field.


• name should be taken from Programs.name field.


Note that you should select all the programs even if they have same code and name.


Note: Count duplicate students for this question(i.e., you don't need to use distinct


Q8 (3 marks)


Define a SQL view Q8(code,name,semester) that displays the course that has the highest average mark. To avoid extreme situations, only consider courses which have at least 15 not null mark records (Course_enrolments.mark). The view should return the following details about each course:


• code should be taken from Subjects.code field.


• name should be taken from Subjects.name field.



• semester should be taken from Semesters.name field.




Q9 (3 marks)


Define an SQL view Q9(name,school,email,starting,num_subjects) which gives the details about all of the current Head of School at UNSW. The view should return the following details about each Head:

l their name (use the name field from the People table)


l the school (use the longname field from the OrgUnits table)


l their email address (use the email field from Staff table)

People<