Write SQL queries to solve a mystery.

A Mystery in Fiftyville

The CS50 Duck has been stolen! The town of Fiftyville has called upon you to solve the mystery of the stolen duck. Authorities believe that the thief stole the duck and then, shortly afterwards, took a flight out of town with the help of an accomplice. Your goal is to identify:

  • Who the thief is,
  • What city the thief escaped to, and
  • Who the thief’s accomplice is who helped them escape

All you know is that the theft took place on July 28, 2021 and that it took place on Humphrey Street.

How will you go about solving this mystery? The Fiftyville authorities have taken some of the town’s records from around the time of the theft and prepared a SQLite database for you, fiftyville.db, which contains tables of data from around the town. You can query that table using SQL SELECT queries to access the data of interest to you. Using just the information in the database, your task is to solve the mystery.

Accepting this Assignment

  1. Accept this assignment via GitHub Classroom.
  2. After about a minute, refresh the page and ensure you see “You’re ready to go!”.

Getting Started

Log into, click on your terminal window, and execute cd by itself. You should find that your terminal window’s prompt resembles the below:


Next execute

get50 fiftyville

in order to download a directory called fiftyville into your codespace.

Then execute

cd fiftyville

in order to change into that directory. Your prompt should now resemble the below:

fiftyville/ $

Execute ls by itself, and you should see a few files:

answers.txt  fiftyville.db  log.sql

If you run into any trouble, follow these same steps again and see if you can determine where you went wrong!


For this problem, equally as important as solving the mystery itself is the process that you use to solve the mystery. In log.sql, keep a log of all SQL queries that you run on the database. Above each query, label each with a comment (in SQL, comments are any lines that begin with --) describing why you’re running the query and/or what information you’re hoping to get out of that particular query. You can use comments in the log file to add additional notes about your thought process as you solve the mystery: ultimately, this file should serve as evidence of the process you used to identify the thief!

As you write your queries, you may notice that some of them can become quite complex. To help keep your queries readable, see principles of good style at The indentation section may be particularly helpful!

Once you solve the mystery, complete each of the lines in answers.txt by filling in the name of the thief, the city that the thief escaped to, and the name of the thief’s accomplice who helped them escape town. (Be sure not to change any of the existing text in the file or to add any other lines to the file!)

Ultimately, you should submit both your log.sql and answers.txt files.



  • Execute sqlite3 fiftyville.db to begin running queries on the database.
    • While running sqlite3, executing .tables will list all of the tables in the database.
    • While running sqlite3, executing .schema TABLE_NAME, where TABLE_NAME is the name of a table in the database, will show you the CREATE TABLE command used to create the table. This can be helpful for knowing which columns to query!
  • You may find it helpful to start with the crime_scene_reports table. Start by looking for a crime scene report that matches the date and the location of the crime.
  • See this SQL keywords reference for some SQL syntax that may be helpful!


Execute the below to evaluate the correctness of your code using check50.

check50 cs50/problems/2021/fall/fiftyville

How to Submit

In your terminal window, execute the below.

submit50 fiftyville

You may submit as many times as you would like up until the deadline. To confirm your submission, go to, where USERNAME is your GitHub username. You should see the code from your latest submission.


Inspired by another case over at SQL City.