# 数据库代写 | Computer Science and Engineering CS6083, Spring 2020

NYU Tandon School of Engineering March 1, 2020
Computer Science and Engineering
CS6083, Spring 2020
Problem Set #2 (due March 13)
Problem 1:
In this problem, you have to write SQL and RA queries for the bakery database already seen in class. Here are the
tables:
Customer (custid, custname, ccn, cphoneno, address, city, zip);
Cake (cakeid, cakename, slices, status, price);
Ingredient (ingredid, iname, price, available);
Contain (cakeid, ingredid, qty);
Orders (custid, cakeid, ordertime, pickuptime, pricepaid);
The bakery offers different types of cakes. A cake has a name, current price, and number of slices (servings) per
cake. Customers need to make orders one day or more in advance, and then pick them up on the agreed day. Each
cake contains a number of ingredients (e.g., flour, sugar, eggs) that are needed to make it. The Contain table states
how much of each ingredient is needed for each cake, while the Ingredient table stores the cost per pound, and the
number of pounds available, of each ingredient. Finally, table Cake has a field status that can be set to either
available or discontinued, depending on whether a cake is still being offered, or has been discontinued. The
ordertime and pickuptime attributes should store both time and date information.
(a) Draw an ER diagram that models this relational schema. Identify any weak entities, and the cardinalities of all
the relationships.
(b) Create the above schema in a database system, choose appropriate attributes types, and define primary keys,
foreign keys and other constraints. Data for this schema will be made available on NYU Classes, so use that
data. Load the data into the database using either insert statements or the bulk load facilities. You may use any
relational database system, as long as it supports basic SQL, views, and some sort of triggers (needed below).
(c) Write the following SQL queries and execute them on your database. Show the queries and the results:
(i) For each cake, list the number of orders for this cake made during 2014.
(ii) Output the cake that is currently the most expensive per slice.
(iii) List any cake that was ordered less than ten times in 2014.
(iv) Output the names of any cakes whose current price is less than twice the total cost of its ingredients.
(v) List the ID and name of any customer from Chicago who has ordered a cake containing peanuts.
(vi) Output the names of any pairs of cakes that share at least three ingredients (even if they use different
amounts of these ingredients).
(vii) For each ingredient, list how many pounds were used for cakes ordered in May 2015.
(viii) Output the name of any customer who has ordered every currently available cake at least once.
(d) Write expressions in Relational Algebra for queries (iv) to viii.
(d) Write SQL statements to perform the following updates to the database:
(i) For any cake currently costing less than twice the cost of its ingredients, raise its current price to twice the
cost of ingredients.
(ii) For every costumer who spent at least \$100 on cakes ordered during 2015, give them a free apple pie by
inserting a new tuple into the Orders table with a price of \$0 and a pickup date of October 10.
(iii) For any cake that has not been ordered for 6 months, set the status of the cake to discontinued.
(e) Consider query (ii) of part (d) again. Can you implement these tasks via triggers, so that an order for a free apple
pie is automatically generated as soon as a customer reaches \$100 of orders during 2015? How about query (iii)?
Can you get the system to automatically change the cake status somehow? Implement and execute these tasks, or
discuss why you cannot do this.
Problems 2:
In this problem, you have to create views and then write queries on the views, for a Video Rental Chain database
that will also be discussed in class. The tables will be made available on NYU Classes, and you have to execute
Customer (cid, came, caddress, cphone, ccn);
Movie (mid, title, genre, year);
Copy (copyid, mid, bid);
Rental (cid, copyid, outdate, returndate, cost);
(a) Define a view that contains for each branch and each movie the information about how many copies of the
movie are currently available in that branch (not checked out). The view should have the attributed bid, mid,
title, and numcopies. Using this view, answer the following queries:
(i) Output the bid of the branch that has the most copies of the movie Godfather available.
(ii) For each movie, output the total number of copies available overall (across all branches).

(b) Define a view on top of the Movie table that contains only the mid, title, and year, but not the genre. Then write
queries using only this view, or explain if you cannot do so:
(i) Add a record to the underlying Movie table with title Minions, mid 6672, and year 2015.
(ii) Delete all movies made in 1966 from the Movie table.
(iii) Delete all movies from the genre science fiction from the Movie table.
(iv) For each year, list the number of movies from that year.
Problem 3:
In this problem you have to design a database for the NYC Department of Health and Mental Hygiene (DOH) that
models restaurant inspections and the grades that restaurants get when they are inspected. Here is the somewhat
simplified scenario you have to model: DOH employs inspectors that visit restaurants unannounced to check if the
restaurant is clean and if the food is handled safely. Each inspector has an ID, a name, and a date when she was
hired. Each restaurant has a unique ID, a name, an address, a phone number, and an owner (a person or company
responsible for it). Owners have IDs, names, and a contact phone number. An owner may of course own a number
of restaurants.
When an inspection occurs, the inspector will check for certain violations, for example “restroom dirty”, “meat is
stored outside refrigerator”, “rats in kitchen”, or “cook did not wear gloves”. Each type of violation comes with a
certain number of penalty points, e.g., 2 points for a dirty restroom but 5 points for meat stored outside the
refrigerator (since this is more dangerous in terms of health). Each type of violation has a code (ID), a description
(e.g., “rats in kitchen”), and a number of penalty points for it. (For simplicity, we assume that violations either occur
or not – in real life there might be different numbers of penalty points, say, for a slightly dirty versus very dirty
restroom.) Your database needs to store the time and date of an inspection, the inspector, the restaurant, and also
which violations were discovered during the inspection. Finally, for each restaurant there is a health grade, say, A
for less than 4 penalty points, B for 5 to 10 points, C for 11 to 15, and FAIL for more than 15. This information
about the grades and points required for a grade should also be stored in the database, so that the current grade of a
restaurant can be computed directly from the data about the last inspection.
(a) Design a database for the above scenario using the ER model. Draw the ER diagram, show the cardinalities of
all relationships, and identify primary keys and any weak entities.
(b) Convert your ER diagram into a relational schema. Identify all tables, attributes, primary keys, and foreign keys.
(c) Write SQL queries for the following questions. If you cannot answer a query using your schema, then you have
to modify your solutions in (a) and (b) appropriately.
(i) For each inspector, output her ID and the average number of penalty points she gave for inspections in 2014.
(ii) For each restaurant, output the name and address and the health grade based on the last inspection. (Note
that this health grade should be computed from the violation data, and not precomputed and stored in the tables.)
(iii) List the name and address of the dirtiest restaurant in NYC, i.e., the one with the most penalty points in the
most recent inspection
(iv) Output the names of any owners that own at least 2 restaurants and where all their restaurants had rats in
the kitchen during the last inspection.
(d) Create tables in the database system, and insert some sample data (say, 5-10 tuples per table, but choose an
interesting data set, so that queries do not output empty results.). Then execute the queries in (c) and submit a log.

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