Midterm Exam ANSWER KEY

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1 CS 461, Database Systems Midterm Exam ANSWER KEY Problem 1: Business rules to ER diagrams For each question below, draw an ER diagram that correctly represents the business rules. Assume that the only business rules that hold are those stated, and that no additional business rules hold. Clearly mark all key and participation constraints using the notation presented in class. (a) Countries host Olympics. A country is identified by its. Olympics are identified by a year in which they are held and the season (Winter or Summer). Each Olympics is hosted by a specific country. We only record countries that hosted Olympics in our database. A country may host multiple Olympics (e.g., Japan hosted the Winter Olympics in 1998 and in 1972), and all such occurrences must be recorded. (b) A dish combines two or more ingredients by cooking them using some cooking method, at some temperature. Dishes, ingredients and cooking methods all have unique s. Ingredients are additionally described by a calorie count per unit weight. Each dish is prepared using at most one cooking method. Only ingredients that are used in some dish are recorded in our database. Participation on Dishes in combine is also OK. 1

2 (c) Bands, identified by a and a year in which they were formed, go on tours. A tour is described by a and is associated with a start and end dates. You may assume that tour dates for a particular band do not overlap (i.e., a band is on at most one tour on any particular day). Further, assume that if a band is removed from our database, then so are all of that band's tours. Problem 2: ER diagrams to SQL Give a translation of the ER diagram below into the relational model. Create as many tables as is necessary. Clearly state whether your translation implements all business rules specified by the diagram. If a rule cannot be implemented, state so clearly. (a) Musicians record title Albums Producers produce create table Musicians ( varchar(64) primary key); create table Producers ( varchar(64) primary key); create table Albums ( title varchar(128) primary key, producer_ varchar(64) not null, foreign key (producer_) references Producers()); create table Albums_Musicians ( album_title varchar(128), musician_ varchar(64), primary key (album_title, musician_), foreign key (album_title) references Albums(title), foreign key (musician_) references Musicians()); Note that participation on Albums in record is not implemented. Participation without a key constraint cannot be implemented in the relational model (without triggers). 2

3 (b) title Bands record Albums contain title Songs create table Bands ( varchar(64) primary key ); create table Albums ( title varchar(128) primary key, band_ varchar(64) not null, foreign key (band_) references Bands () ); create table Songs ( title varchar(128), album_title varchar(128), primary key (title, album_title), foreign key (album_title) references Albums (title) on delete cascade ); (c) num Phones addr have People Addresses live_at create table Phones ( num varchar(16) primary key); create table Addresses ( 3

4 addr varchar(128) primary key); create table People ( varchar(64) primary key, phone varchar(16) not null, addr varchar(128) not null, foreign key (phone) references Phones(num), foreign key (addr) references Addresses (addr)); Problem 3 (30 points) Relational algebra and SQL Items (product, brand, price) product brand price diapers 7Gen $45 wipes 7Gen $20 soap 7Gen $5 cream Weleda $8 shoes Camper $55 book Penguin $12 boots Camper $42 pants Gap $15 tshirt Gap $10 socks Gap $5 hat Gap $13 Orders (product, customer, quantity) product customer quantity diapers Ann 3 diapers Bob 2 diapers Jane 1 wipes Ann 1 book Ann 3 book Dave 2 boots Bob 1 pants Bob 2 pants Ann 3 socks Dave 4 hat Dave 2 hat Jane 2 (a) (10 points) Write a SQL query that lists customers who purchased both a 7Gen product and a Gap product. Result should have the schema (customer). Both options below are correct. I will not insist on distinct for the first option, i.e., it s OK to return the of the same custromer more than once. Option 1: select distinct O1.customer from Orders O1, Orders O2, Items I1, Items I2 where O1.customer = O2.customer and O1.product = I1.product and O2.product = I2.product and I1.brand = '7Gen' and I2.brand = 'Gap' 4

5 Option 2: select O.customer from Orders O, Items I where O.product = I.product and I.brand = '7Gen' INTERSECT select O.customer from Orders O, Items I where O.product = I.product and I.brand = 'Gap' (b) (10 points) Write a SQL query that lists pairs of products by the same brand that were purchased by different customers. List each pair exactly once, i.e., your query should not list both "Ann, Dave, Gap" and "Dave, Ann, Gap", and it should not list "Ann, Dave, Gap" more than once. Result should have the schema (customer1, customer2, brand). Either of these options is fine (the query is worded inconsistently, these are two possible interpretations). Option 1: select O1.customer as customer1, O2.customer as customer1, I1.brand from Items I1, Items I2, Orders O1, Orders O2 where I1.product = O1.product and I2.product = O2.product and I1.brand = I2.brand and O1.customer < O2.customer Option 2: select I1.product as product1, I2.product as product2, O1.customer as customer1, O2.customer as customer2, I1.brand from Items I1, Items I2, Orders O1, Orders O2 where I1.product = O1.product and I2.product = O2.product and I1.brand = I2.brand and O1.customer < O2.customer (c) (10 points) Write a SQL query that computes total sales per brand. Sort results by total sales. Result should have the schema (brand, sales). select I.brand, sum(price * quantity) from Items I, Orders O where I.product = O.product group by I.brand 5

6 (d) (10 points) Write a SQL query that list the total quantity of products purchased per brand, for products that cost $15 or more. Sort results by brand. Result should have the schema (brand, quantity). select I.brand, sum(quantity) as quantity from Items I, Orders O where I.product = O.product and I.price >= 15 group by I.brand order by I.brand (e) (10 points) Write a relational algebra expression that returns s of customers who purchased a 7Gen product but did not purchase a hat. π customer (O (σ brand=7gen I)) π customer (σ product=hat O) (f) (10 points) Write a relational algebra expression that returns brands that were purchased by Ann but not by Bob. π brand (I (σ customer=ann O)) π brand (I (σ customer=bob O)) 6