This worksheet focuses on SQLite databases.
These things might be helpful while working on the problems. Remember that for worksheets, we don't strictly limit what resources you can consult, so these are only suggestions.
The main references for these topics are:
You'll need to complete these before you can work on the worksheet.
Quiz 12 will also be impossible to work on until you've successfully completed these steps.
There's nothing to install if you just want to use SQLite with Python, as the module
sqlite3 is already part of the Python standard library.
However, if you just want to run one SQL query and show the results, a fairly long Python program is needed. It's much easier if you can install the SQLite REPL (or "command line shell") that lets you run queries directly from a prompt in your terminal. This worksheet assumes you have the command line shell for SQLite.
Lectures 30 and 32 discussed how to install this. Here is a quick video showing the steps to install in Windows 10:
Here are more detailed written installation instructions by platform.
If you use Windows, you need to install it yourself. The installation doesn't look like the graphical ones you may be used to, with a window and buttons guiding you through the steps. Instead you download a zip file and extract it. The whole thing is relatively quick, but the steps below are described in some detail, so the written instructions are a bit long. (Consider just watching the 1-minute video and following along instead.)
sqlite-tools-win32-x86-. The description next to the link should begin: A bundle of command-line tools for managing SQLite database files
sqlite-tools-win32-x86-3380200. Double click to enter that folder.
You should now see a list of three files, named
.exe may be missing if explorer is configured to hide file extensions (the default).
sqlite3.exeis the only one you want. Drag that file to the desktop to extract a copy of it.
sqlite3icon on the desktop. Don't click it; we'll work in the terminal instead.
cd C:\Users\myusername\OneDrive\Desktop, depding on where PowerShell opens and whether you use OneDrive desktop backup)
.exitto return to PowerShell
& 'C:\Users\My Username Has Spaces\Desktop\sqlite3.exe'
If you use Linux or MacOS, SQLite's command line shell is almost always pre-installed. Type
sqlite3 in a terminal and press enter. Success (meaning it is already installed) looks something like this:
sqlite3 SQLite version 3.31.1 2020-01-27 19:55:54 Enter ".help" for usage hints. Connected to a transient in-memory database. Use ".open FILENAME" to reopen on a persistent database. sqlite>
(at which point you'd want to exit using command
Failure (meaning it is not already installed) looks something like this:
$ sqlite3 sqlite3: command not found
If you use Linux or MacOS and SQLite's command line shell is not already installed, contact your TA or instructor for help.
Any time you have your terminal open, there are three situations you may find yourself in:
The Python REPL is running, and waiting for a Python statement from you. If this is the case, you'll see a prompt
and you can quit back to the terminal using the command
The SQLite command line shell is running, and is waiting for a SQL command from you. If this is the case, you'll see a prompt
and you can quit back to the terminal using the command
|When running||prompt looks like||exit with||and then|
||back to terminal|
||back to terminal|
Questions 1 uses the HYG star database discussed in Lecture 32. You
So you'll need to download this and put the file in a place where you can find it.
The only table in this database is called
stars, and the columns present in that table are described at
hyg_data.sqliteas the first command line argument, e.g. a typical Windows command for PowerShell would be
and a typical Linux or MacOS terminal command would be
After pressing enter, you should see that SQLite is running and waiting for a command with the prompt
If everything is working, the output should look like this:
SELECT COUNT(*) FROM stars;
If you instead see this:
sqlite> SELECT COUNT(*) FROM stars; 119614 sqlite>
then it means you ran
sqlite> SELECT COUNT(*) FROM stars; Error: no such table: stars sqlite>
sqlite3successfully, but in a directory that didn't contain the star database. That directory will now contain an empty file named
hyg_data.sqlite, which you should probably find and remove to prevent yourself from later confusing it with the actual database file.
Use SQL queries run against the HYG star database to answer these questions. (You should consider both the query and its return value as part of the answer.)
What are the
ids, color indices (
ci), and names (
proper) of the five dimmest stars in the database (as measured by
Find the positions (as
(ra,dec) coordinates) of the ten "most blue" stars that don't have proper names in the database. (The column
ci is proportional to how blue a star is, so large values in that column mean very blue.)
There is a new SQLite feature (or more precisely, a feature of the SQL dialect that SQLite uses for queries) that you'll need to use in this problem.
In many places where we've used column names in our queries, you can also use expressions that apply arithmetic operators and other functions to the values in the columns. For example, if a database of MCS 275 grades has columns called
project4pct, then this query would return the email addresses of students whose grades on those two projects differed by more than 10 percent:
SELECT email FROM mcs275roster WHERE ABS(project3pct - project4pct) > 10;
You can also use expressions like this in the requested list of output columns. For example, this query would get the average of project 3 and 4 percentages for all students, listed in alphabetical order by last name.
SELECT lastname, firstname, 0.5*(project3pct + project4pct) FROM mcs275roster ORDER BY lastname;
Such expressions can also be used after
ORDER BY to make a custom sort.
You can find lists of built-in functions in SQLite in the documentation:
Write a program that stores, delivers, and ranks programming jokes using a SQLite database. It should support three operations:
The program should create the database and table it needs if they don't already exist. Otherwise, it should open and use the existing database.
The three functions should be selected using command line arguments. The first command line argument is always the command---one of
best. If the command is
add, then a second command line argument is required, which is the joke itself. If the command is
tell, no other arguments are required but the user is prompted for their approval/disapproval of the joke through keyboard input.
rowidthat has a distinct integer value for each row. This is a primary key. It won't return this column unless you ask for it explicitly (e.g.
SELECT * FROM ...won't show it, but
SELECT rowid FROM ...or
SELECT rowid,* FROM ...will. Having a unique id for each row is helpful so you can retrieve a row, and then apply an operation to the same row later.
RANDOM()that will return a random number for each row, and you order by that.
Bboth have type integer then
A/Bcomputes the integer division of
B. In contrast,
1.0*A/Bwould give the true quotient because the multiplication by 1.0 converts
Ato a float (or
REAL, in SQLite terminology).
Save the program as
Here is a sample session of what using it should look like. (These are from a linux terminal session, where the terminal prompt is "$". In Windows PowerShell, the prompt will look a bit different.)
$ python3 jokedb.py tell ERROR: No jokes in database. [... omitted: several jokes are added ...] $ python3 jokedb.py tell There are 10 types of people in the world: Those who understand binary, and those who don't. Were you amused by this? (Y/N)y $ python3 jokedb.py tell The two hardest things in programming are naming things, cache invalidation, and off-by-one errors. Were you amused by this? (Y/N)n $ python3 jokedb.py add "Most people agree that there were no widely-used high-level programming languages before FORTRAN. Unfortunately, there is no agreement on whether this makes FORTRAN the 1st such language, or the 0th." $ python3 jokedb.py tell After learning Python, my kids stopped saying 'I won't take out the garbage!'. Instead, they say 'take_out_garbage() is deprecated in v2.0'. Were you amused by this? (Y/N)y $ python3 jokedb.py best ------------------------------------------------------- #1 with 100% success rate after 8 tellings: Knock knock. Race condition. Who's there? ------------------------------------------------------- #2 with 71% success rate after 7 tellings: There are 10 types of people in the world: Those who understand binary, and those who don't. ------------------------------------------------------- #3 with 67% success rate after 6 tellings: A software testing engineer walks into a bar and orders a refrigerator, -1 glasses of water, and INT_MAX+1 cans of soda. ------------------------------------------------------- #4 with 60% success rate after 5 tellings: After learning Python, my kids stopped saying 'I won't take out the garbage!'. Instead, they say 'take_out_garbage() is deprecated in v2.0'. ------------------------------------------------------- #5 with 50% success rate after 4 tellings: The two hardest things in programming are naming things, cache invalidation, and off-by-one errors. $
This is another SQLite feature to know about (which will be helpful in this problem).
When you make a SELECT query, if you only want to know how many rows would be returned, and not the actual data, you can ask for
in place of the list of columns you would otherwise include. For example,
SELECT COUNT(*) FROM mcs275roster WHERE project4pct >= 90;
might return the number of students who scored 90 percent or higher on project 4.
mag is a column indicating the apparent brightness of the star as seen from earth, this is not the same as the amount of light a star emits. Some stars seem dim only because they are very far from the earth. To account for this, the column
absmag (absolute magnitude) indicates the brightness of the star if it were observed from a certain standard distance (about 32 light-years). Thus
absmag is a measure of the light energy output of the star. Both
absmag use a scale where smaller numbers correspond to more light energy.
The brightest star in the night sky is Sirius. But how many stars in this database actually emit more light than Sirius (and appear dimmer due to being farther away)?
Of those, what fraction are less blue than Sirius?
What named star the database has energy output closest to that of the sun?