hw2 release

hw2/hw2.md

+# CSE 344 Homework 2: Basic SQL Queries
+ 
+**Objectives:** To create and import databases and to practice simple SQL queries using SQLite.
+
+**Assignment tools:** [SQLite 3](https://www.sqlite.org/), the flights dataset hosted in `hw2` directory
+on gitlab.
+(Reminder: To extract the content of a tar file, try the following command on a linux machine: 
+`tar zxvf flights-small.tar.gz`)
+
+**Assigned date:** Wednesday, January 17, 2018
+
+**Due date:** Wednesday, January 24 at 11:30pm. You have 1 week for this assignment. Turn in your solution using `git`. 
+
+**Questions:** Make sure your post them on [Piazza](https://piazza.com/class/j7zs8a2vwwp17n). 
+
+**What to turn in:**
+
+`create-tables.sql` and `hw2-q1.sql`, `hw2-q2.sql`, etc (see below).
+
+**Resources:** 
+
+Prof. Cheung's research group has been working on a tool called [Scythe](https://courses.cs.washington.edu/courses/cse344/tools/scythe/)
+that allows you to generate
+SQL given input/output examples. Feel free to use it to learn SQL syntax. This is entirely optional and 
+is not "officially supported." Also, it is meant to be a 
+learning tool and not to do your homework for you! If you just turn in the SQL generated by Scythe, you will 
+very likely get 0 points for the assignment (not to mention that the generated SQL might not even be correct...).
+
+## Assignment Details
+
+In this homework, you will write several SQL queries on a relational flights database. 
+The data in this database is abridged from the [Bureau of Transportation Statistics](http://www.transtats.bts.gov/DL_SelectFields.asp?Table_ID=236&DB_Short_Name=On-Time) 
+The database consists of four tables:
+
+```SQL
+FLIGHTS (fid int, year int, month_id int, day_of_month int, 
+         day_of_week_id int, carrier_id varchar(3), flight_num int,
+         origin_city varchar(34), origin_state varchar(47), 
+         dest_city varchar(34), dest_state varchar(46), 
+         departure_delay double, taxi_out double, arrival_delay double,
+         canceled int, actual_time double, distance double, capacity int, 
+         price double)
+CARRIERS (cid varchar(3), name varchar(83))
+MONTHS (mid int, month varchar(9))
+WEEKDAYS (did int, day_of_week varchar(9))
+```
+
+(FYI All data except for the capacity and price columns are real.) 
+We leave it up to you to decide how to declare these tables and translate their types to sqlite. 
+But make sure that your relations include all the attributes listed above.
+
+In addition, make sure you impose the following constraints to the tables above:
+- The primary key of the `FLIGHTS` table is `fid`.
+- The primary keys for the other tables are `cid`, `mid`, and `did` respectively.
+- `Flights.carrier_id` references `Carrier.cid`
+- `Flights.month_id` references `Months.mid`
+- `Flights.day_of_week_id` references `Weekdays.did`
+
+We provide the flights database as a set of plain-text data files in the linked 
+`.tar.gz` archive. Each file in this archive contains all the rows for the named table, one row per line.
+
+In this homework, you need to do two things:
+1. import the flights dataset into SQLite
+2. run SQL queries to answer a set of questions about the data.
+
+
+### IMPORTING THE FLIGHTS DATABASE (20 points)
+
+To import the flights database into SQLite, you will need to run sqlite3 with a new database file.
+for example `sqlite3 hw2.db`. Then you can run `CREATE TABLE` statement to create the tables, 
+choosing appropriate types for each column and specifying all key constraints as described above:
+
+```
+CREATE TABLE table_name ( ... );
+```
+
+Currently, SQLite does not enforce foreign keys by default. 
+To enable foreign keys use the following command. 
+The command will have no effect if your version of SQLite was not compiled with foreign keys enabled. 
+In that case do not worry about it (i.e., you will need to enforce foreign key constraints yourself as 
+you insert data into the table).
+
+```
+PRAGMA foreign_keys=ON;
+```
+
+Then, you can use the SQLite `.import` command to read data from each text file into its table:
+
+```
+.import filename tablename
+```
+
+See examples of `.import` statements in the lecture and section notes, and also look at the SQLite 
+documentation or sqlite3's help online for details.
+
+Put all the code for this part (four `create table` statements and four `.import` statements) 
+into a file called `create-tables.sql` inside the `hw2/submission` directory.
+
+### Writing SQL QUERIES (80 points, 10 points each)
+
+**HINT: You should be able to answer all the questions below with SQL queries that do NOT 
+contain any subqueries!**
+
+For each question below, write a single SQL query to answer that question.
+Put each of your queries in a separate `.sql` file as in HW1, i.e., `hw2-q1.sql`, `hw2-q2.sql`, etc.
+
+**Important: The predicates in your queries should correspond to the English descriptions. 
+For example, if a question asks you to find flights by Alaska Airlines Inc., the query should 
+include a predicate that checks for that specific name as opposed to checking for the matching carrier ID. 
+Same for predicates over months, weekdays, etc.
+
+Also, make sure you name the output columns as indicated as we will be grading your assignment using 
+scripts.**
+
+In the following questions below flights **include canceled flights as well, unless otherwise noted.** 
+Also, when asked to output times you can report them in minutes and don’t need to do minute-hour conversion.
+You may assume that when linking flights that you do not need to be concerned about exact arrival and departure times
+(you only need to evaluate dates).
+
+If a query uses a `GROUP BY` clause, make sure that all attributes in your `SELECT` clause for that query 
+are either grouping keys or aggregate values. SQLite will let you select other attributes but that is wrong
+as we discussed in lectures. Other database systems would reject the query in that case. That said we will
+be enforcing SQL Server syntax.
+
+
+1. (10 points) List the distinct flight numbers of all flights from Seattle to Boston by Alaska Airlines Inc. on Mondays. 
+Also notice that, in the database, the city names include the state. So Seattle appears as 
+Seattle WA.  
+   Name the output column `flight_num`.    
+   [Hint: Output relation cardinality: 3 rows]
+
+2. (10 points) Find all flights from Seattle to Boston on July 15th 2015. Search only for itineraries that have one stop. 
+Both legs of the flight must have occurred on the same day (same day here means the date of the flight). 
+It’s fine if the landing date is different from the flight date, say in the case of an overnight flight, 
+and must be with the same carrier. In other words all legs of the flights must start on the same day 
+(the day they land doesn't matter) and all trips must be with the same carrier (i.e. no switching airlines 
+during your layover). The total flight time (`actual_time`) of the entire itinerary should be fewer than 7 hours 
+(but notice that actual_time is in minutes). 
+   For each itinerary, the query should return the name of the carrier, the first flight number, 
+the origin and destination of that first flight, the flight time, the second flight number, 
+the origin and destination of the second flight, the second flight time, and finally the total flight time. 
+Only count flight times here; do not include any layover time.   
+   Name the output columns `name` as the name of the carrier, `f1_flight_num`, `f1_origin_city`, `f1_dest_city`, `f1_actual_time`, `f2_flight_num`, `f2_origin_city`, `f2_dest_city`, `f2_actual_time`, and `actual_time` as the total flight time. List the output columns in this order.
+   [Output relation cardinality: 488 rows]
+
+
+3. (10 points) Find the day of the week with the longest average arrival delay. 
+Return the name of the day and the average delay.   
+   Name the output columns `day_of_week` and `delay`, in that order. (Hint: consider using `LIMIT`. Look up what it does!)   
+   [Output relation cardinality: 1 row]
+
+
+4. (10 points) Find the names of all airlines that ever flew more than 1000 flights in one day 
+(i.e., a specific day/month/year, but not any 24-hour period). 
+Return only the names of the airlines. Do not return any duplicates 
+(i.e., airlines with the exact same name).    
+   Name the output column `name`.   
+   [Output relation cardinality: 11 rows]
+
+
+5. (10 points) Find all airlines that had more than 0.5 percent of their flights out of Seattle be canceled. 
+Return the name of the airline and the percentage of canceled flight out of Seattle. 
+Order the results by the percentage of canceled flights in ascending order.    
+   Name the output columns `name` and `percent`, in that order.   
+   [Output relation cardinality: 6 rows]
+
+
+6. (10 points) Find the average price of tickets between Seattle and New York, NY in the entire month. 
+Show the average price for each airline separately.   
+   Name the output columns `carrier` and `average_price`, in that order.   
+   [Output relation cardinality: 3]
+
+
+7. (10 points) Find the total capacity of all direct flights that fly between Seattle and San Francisco, CA on July 10th, 2015.   
+   Name the output column `capacity`.   
+   [Output relation cardinality: 1]
+   
+   
+8. (10 points) Compute the total departure delay of each airline 
+across all flights in the entire month.
+   Name the output columns `name` and `delay`, in that order.
+   [Output relation cardinality: 22]
+
+
+### Programming style 
+To encourage good SQL programming style please follow these two simple style rules:
+
+- Give explicit names to all tables referenced in the `FROM` clause.
+For instance, instead of writing:
+   ``` 
+   select * from flights, carriers where carrier_id = cid
+   ```
+   write
+   ```
+    select * from flights as F, carriers as C where F.carrier_id = C.cid
+   ```
+   So that it is clear which table you are referring to.
+
+
+- Similarly, reference to all attributes must be qualified by the table name.
+Instead of writing:
+   ```
+   select * from flights where fid = 1
+   ```
+   write
+   ```
+   select * from flights as F where F.fid = 1
+   ```
+   This will be useful when you write queries involving self joins.
+
+
+## Submission Instructions
+Answer each of the queries above and put your SQL query in a separate file. 
+Call them `hw2-q1.sql`, `hw2-q2.sql`, etc. Make sure you name the files exactly as is. Put your 
+`.sql` files inside `hw2/submission` (along with your `create-tables.sql` from 
+the first part of this assignment).
+ 	
+Like HW1, you may submit your code multiple times; we will use the latest version you submit that 
+arrives before the deadline. 
+
+**Important**: To remind you, in order for your answers to be added to the git repo, 
+you need to explicitly add each file:
+
+```sh
+$ git add hw2-q1.sql hw2-q2.sql ...
+```
+
+**Again, just because your code has been committed on your local machine does not mean that it has been 
+submitted -- it needs to be on GitLab!**
+
+Use the same bash script `turnInHw.sh` in the root level directory of your repository that 
+commits your changes, deletes any prior tag for the current lab, tags the current commit,
+and pushes the branch and tag to GitLab. 
+
+If you are using Linux or Mac OSX, you should be able to run the following:
+
+```sh
+$ ./turnInHw.sh hw2
+```
+
+You should see something like the following output:
+
+```sh
+$ ./turnInHw.sh hw2
+[master b155ba0] Lab 2
+ 1 file changed, 1 insertion(+)
+Deleted tag 'hw2' (was b26abd0)
+To git@gitlab.com:cse344-2017au/cse344-[your CSE username].git
+ - [deleted]         hw2
+Counting objects: 11, done.
+Delta compression using up to 4 threads.
+Compressing objects: 100% (4/4), done.
+Writing objects: 100% (6/6), 448 bytes | 0 bytes/s, done.
+Total 6 (delta 3), reused 0 (delta 0)
+To git@gitlab.com:cse344-2017au/cse344-[your CSE username].git
+   ae31bce..b155ba0  master -> master
+Counting objects: 1, done.
+Writing objects: 100% (1/1), 152 bytes | 0 bytes/s, done.
+Total 1 (delta 0), reused 0 (delta 0)
+To git@gitlab.com:cse344-2017au/cse344-[your CSE username].git
+ * [new tag]         hw2 -> hw2
+```

hw2/starter-code/months.csv

+1,January
+2,February
+3,March
+4,April
+5,May
+6,June
+7,July
+8,August
+9,September
+10,October
+11,November
+12,December

hw2/starter-code/weekdays.csv

+1,Monday
+2,Tuesday
+3,Wednesday
+4,Thursday
+5,Friday
+6,Saturday
+7,Sunday
+9,Unknown

hw2/submission/README

+put your .sql files in this directory, one file per question.