辅导INFO20003、讲解Query Optimisation、SQL设计辅导、讲解SQL程序
解析Haskell程序|讲解留学生Proc
INFO20003 Semester 1, 2019
Assignment 3 – Query Processing and Query Optimisation
Due: 6:00pm Friday 24 May
Submission: Via LMS https://lms.unimelb.edu.au
Weighting: 10% of your total assessment. The assignment will be graded
out of 20 marks.
Question 1 (5 marks)
Consider two relations called Item and OrderItem. Imagine that relation Item has 160,000
tuples and OrderItem has 200,000 tuples. Both relations store 100 tuples per a page. Consider
the following SQL statement:
SELECT *
FROM Item INNER JOIN OrderItem
ON Item.ItemID = OrderItem.ItemID;
We wish to evaluate an equijoin between OrderItem and Item, with an equality condition
Item.ItemID = OrderItem.ItemID. There are 802 buffer pages available in memory for this
operation. Both relations are stored as (unsorted) heap files. Neither relation has any indexes
built on it.
Consider the alternative join strategies described below and calculate the cost of each
alternative. Evaluate the algorithms using the number of disk I/O's (i.e. pages) as the cost. For
each strategy, provide the formulae you use to calculate your cost estimates.
a) Page-oriented Nested Loops Join. Consider Item as the outer relation. (1 mark)
b) Block-oriented Nested Loops Join. Consider Item as the outer relation. (1 mark)
c) Sort-Merge Join. Assume that Sort-Merge Join can be done in 2 passes. (1 mark)
d) Hash Join. (1 mark)
e) What would be the lowest possible cost to perform this query, assuming that no
indexes are built on any of the two relations, and assuming that sufficient buffer space
is available? What would be the minimum buffer size required to achieve this cost?
Explain briefly. (1 mark)2
Question 2 (5 marks)
Consider a relation with the following schema:
Student (studentid, firstname, lastname, faculty, level, wam)
The Student relation has 800 pages and each page stores 80 tuples. The faculty attribute can
take one of ten values (“Arts”, “Architecture”, “Business”, “Education”, “Fine Arts and Music”,
“Law”, “Medicine”, “Science”, “Agricultural Science”, “Engineering”) and wam (Weighted
Average Mark) can have values between 0 and 100 ([0,100]).
Suppose that the following SQL query is executed frequently using the given relation:
SELECT *
FROM Student
WHERE wam > 75 AND faculty = 'Arts';
Your job is to analyse the query plans and estimate the cost of the best plan utilizing the
information given about different indexes in each part.
a) Compute the estimated result size for the query, and the reduction factor of each filter.
(1 mark)
b) Compute the estimated cost of the best plan assuming that a clustered B+ tree index
on (faculty, wam) is the only index available. Suppose there are 120 index pages.
Discuss and calculate alternative plans. (1 mark)
c) Compute the estimated cost of the best plan assuming that an unclustered B+ tree
index on (wam) is the only index available. Suppose there are 60 index pages. Discuss
and calculate alternative plans. (1 mark)
d) Compute the estimated cost of the best plan assuming that an unclustered Hash index
on (faculty) is the only index available. Discuss and calculate alternative plans.
(1 mark)
e) Compute the estimated cost of the best plan assuming that an unclustered Hash index
on (wam) is the only index available. Discuss and calculate alternative plans.
(1 mark)3
Question 3 (10 marks)
Consider the following relational schema and SQL query. The schema captures information
about customers, their orders, and orderitems.
Customer (cusid: integer, postcode: char(4), name: char(20))
Order (orderid: integer, orderdate: date, cusid: integer, departmentid: integer)
OrderItem (orderitemid: integer, handling: char(20), orderid: integer,
itemname: char(15), quantity: integer)
Consider the following query:
SELECT c.postcode, o.departmentid
FROM Customer c, Order o, OrderItem oi
WHERE c.cusid = o.cusid AND o.orderid = oi.orderid
AND oi.quantity < 10 AND oi.itemname = 'Rotring 600';
The system’s statistics indicate that there are 400 different itemname values, and quantity of
order items range from 0 to 50 ([0,50]). There are a total of 80,000 Orderitems and 8,000
Orders and 2,000 Customers in the database. Each relation fits 100 tuples in a page. Suppose
there exists a clustered B+ tree index on (Order.orderid) of size 20 pages, and suppose there
is a clustered B+ tree index on (Orderitem.quantity) of size 200 pages.
a) Compute the estimated result size and the reduction factors (selectivity) of this query.
(2 marks)
b) Compute the cost of the plans shown below. Assume that sorting of any relation (if
required) can be done in 2 passes. NLJ is a Page-oriented Nested Loops Join.
Assume that cusid is the candidate key of the Customer relation, and orderid is the
candidate key of the Order relation. Assume that 100 tuples of a resulting join between
Customer and Order fit in a page. Similarly, 100 tuples of a resulting join between
Order and OrderItem fit in a page. If selection over filtering predicates is not marked in
the plan, assume it will happen on-the-fly after all joins are performed, as the last
operation in the plan. (8 marks, 2 marks per plan)4
Formatting Requirements:
For each question, present an answer in the following format:
Show the question number before each question. You do not need to include the text of
the question itself.
Show your answer in blue text (please type your answers on a computer).
Start Question 2 and Question 3 on a new page.
For each of the calculations, provide all the formulae you used to calculate your cost
estimates, and show your working, not only the result.
Submission Process:
Submit a single PDF showing your answers to all questions to the Assessment page on LMS
by 6pm on the due date of Friday 24 May. Name your file ‘STUDENT_ID’.pdf, where
STUDENT_ID corresponds to YOUR student id.
Requesting a Submission Deadline Extension
If you need an extension due to a valid (medical) reason, you will need to provide evidence to
support your request by 9pm, Thursday 23 May. Medical certificates need to be at least two
days in length.
To request an extension:
1. Email the head tutor, Alan Thomas (alan.thomas@unimelb.edu.au) from your
university email address, supplying your student ID, the extension request and
supporting evidence.
2. If your submission deadline extension is granted, you will receive an email reply
granting the new submission date. Replies may take up to 12 hours, so please be
patient.
Reminder: INFO20003 Hurdle Requirements
To pass INFO20003 you must pass two hurdles:
Hurdle 1: Obtain at least 50% (15/30) or higher for the three assignments (each worth
10%)
Hurdle 2: Obtain a grade of 50% (35/70) or higher for the End of Semester Exam
Therefore, it is our recommendation to students that you attempt every assignment and every
question in the exam.
GOOD LUCK!