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COMP93211- Project 1: SQL Solved
. 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.
• 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
• PLpgSQL functions are not allowed to use in this project
• For each question, you must output result within 120 seconds on Grieg server.
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, 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/19s1/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, you can download the files: mymyunsw.dump, proj1.sql to get you started. You can grab the check.sql separately, once it becomes available.
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/19s1/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/19s1/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
• 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,longname) that gives the distinct room id and name of any Laboratory room (refers to the Room_types.description) that is used for the course COMP9311 in 2013 S1. The view should return the following details about each room:
• unswid should be taken from Rooms.unswid field.
• longname should be taken from Rooms.longname field.
Q2 (2 marks)
Define a SQL view Q2(unswid,name) that displays unswid and name of all the distinct staff who taught the student Bich Rae. 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.
Q3 (3 marks)
Define a SQL view Q3(unswid,name) that gives all the distinct international students who enrolled in COMP9311 and COMP9021 in the same semester. 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.
Q4 (3 marks)
Define a SQL view Q4(code,name) that displays all the distinct programs (with different ids) which have between 30 (inclusive) to 70 (inclusive) percent of international students. In a program, the percent of international students is defined as the number of distinct international students / the number of all the distinct 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.
Q5 (3 marks)
Define a SQL view Q5(code,name,semester) that displays the course that has the highest minimum mark. To avoid extreme situations, only consider courses which have at least 20 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.
Q6 (3 marks)
Define SQL views Q6(num1,num2,num3), which give the number of, respectively
• distinct local students enrolled in 10S1 in stream(s) named Chemistry.
• distinct international students enrolled in 10S1 in programs offered by Faculty of Engineering.
• all the distinct students enrolled in 10S1 in the Computer Science (3978) program.
Note:
• the student IDs are the UNSW ids (i.e. student numbers) defined in the People.unswid field.
• Do not count duplicate records.
Q7 (4 marks)
Define an SQL view Q7(name,faculty,email,starting,num_subjects) which gives the details about some Dean of Faculty at UNSW. The view should return the following details about each Dean:
⚫ their name (use the name field from the People table)
⚫ the faculty (use the longname field from the OrgUnits table)
⚫ their email address (use the email field from People table)
⚫ the date that they were appointed (use the starting date from the Affiliations table)
⚫ the number of different subjects they have participated as a staff
Since there is some dirty-looking data in the Affiliations table, you will need to ensure that you return only legitimate Head of School. Apply the following filters together:
⚫ only choose people whose role is exactly ‘Dean’
⚫ only choose people for whom this is their primary role ⚫ only choose people who have taught at least one subject.
⚫ only choose organisational units whose type is actually ‘Faculty’ Note:
⚫ Two subjects are different if they have different subject codes
Q8 (4 marks)
UNSW wants to know the most popular subjects. Define a SQL view Q8(subject) that lists the most popular subjects. A subject is one of the most popular subjects if there are at least 20 distinct students enrolled (via the Course_enrolments table) in at least 20 distinct courses offerings of the subject. Each tuple in the view should contain the following:
⚫ the subject code (Subjects.code field) and name (Subjects.name field), in the format e.g. COMP9311 Database Systems (Note that there is a space between subject code and name)
Note:
⚫ Some course offerings have no students enrolled in. It appears in Courses, but not in Course_enrolments.
Q9 (4 marks)
Define SQL view Q9(year, num, unit), which gives, for each unit, the year with the greatest number of distinct international students enrolled, and the number of distinct international students enrolled for this year. The view should return the following details about each unit:
• year should be taken from Semesters.year field.
• num counts the total number of international students enrolled.
• unit should be taken from OrgUnits.longname field. Note:
• you should ignore the units with no international student.
• In the case of ties, the same unit with different years should all be included in the result.
Q10 (4 marks)
Define SQL view Q10(unswid,name,avg_mark), which gives the unswid and name of
students with the top 10 highest rankings in semester 2011 S1. Students’ rankings are ordered by avg_mark (i.e., the average mark of all the courses completed in 2011 S1) from highest to lowest. A student must be a full-time student (complete at least 3 courses in 2011 S1) in order to calculate his/her avg_mark. If there are multiple students with the same avg_mark, they have the same rank, which means your view may contain more than 10 rows. 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.
• avg_mark as numeric (4,2).
Note that for this problem:
• to complete a course, we only consider the students who receive a mark for the course taken.
You may use Course_enrolments.mark >= 0 to retrieve a list of valid students.
• to calculate avg_mark, only consider the courses taken in 2011 S1.
• rank is with gaps. i.e., if there are 2 students ranking first, the third student will be ranked as third.
Q11 (4 marks)
Below are the rules for students’ academic standings:
i. If a student takes more than one course in a semester, his/her academic standing would be ‘Probation’ if none of them passed, ‘Referral’ if 50% or less of the taken courses are passed, and ‘Good’ otherwise.
ii. If a student takes only one course in a semester, he/she will receive ‘Good’ if he/she passes it, and ‘Referral’ if he/she fails it.
Define SQL view Q11(unswid,name,academic_standing), which gives the unswid, name and academic standing of students with the unswid beginning with ‘313’ in 2011 S1. 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.
• academic standing should be defined as the rules given above. You will need to display ‘Good’, ‘Probation’, ‘Referral’ for each student you found.
Note:
• for each student, we only consider the courses in which he/she receives a not null mark.
You may use Course_enrolments.mark >= 0 to retrieve a list of valid students.
• to pass a course, a student needs to get 50 or more in that course.
(Course_enrolments.mark >= 50)
• don’t consider the students who never get any mark from any course in that semester.
Q12 (4 marks)
The head of school would like to know the performance of students in a set of CSE subjects. Subjects in this set have their subject codes starting with “COMP90” and are offered in every major semester (i.e., S1 and S2) in a given period (from 2003 (inclusive) to 2012 (inclusive)). To evaluate the performance of students, the head of school requested to know the PASS rate in every major semester in the given period. The PASS rate is defined as the number of students who have got PASS
(Course_enrolments.mark >= 50) / number of students who have actually received a mark (i.e.
Course_enrolments.mark >= 0). Define an SQL view
Q12(code,name,year,s1_ps_rate,s2_ps_rate) that gives a list of subjects. Each tuple in the view should contain the following:
⚫ the subject code (Subject.code field)
⚫ the subject name (Subject.name field)
⚫ the year (Semesters.year field in the format of the last 2 digits (i.e., 12 for 2012))
⚫ semester 1 PASS rate as numeric (4,2)
⚫ semester 2 PASS rate as numeric (4,2) Note:
• We only consider the students who receive a mark for the course taken. You may use Course_enrolments.mark >= 0 to retrieve a list of valid students.
• Use numeric (4,2) to restrict the precision of the ratios, and be careful about typecasting between integers and reals.
• If in some semesters there exists no students with a mark for a course, just output the pass rate as null in this case.
