Dante O. Cuales, Jr.

[danteocualesjr]

SQL: Structured Query Language

Day 1 Exercises

Preparations

• Refer first to setup.sql to familiarize yourself with the different names of the tables and their corresponding columns and rows.
• Launch SQLite shell/database and specify a persistent DB: sqlite3 mydatabase.db.

Creating/building tables

• Create a table called track that holds information about a music track:

create table track (
...> id integer primary key autoincrement,
...> title varchar(128),
...> album_id integer,
...> foreign key(album_id) references album(id)
...> );

• Create a table called artist_album to connect artists to album:

create table artist_album (
...> artist_id integer,
...> album_id integer,
...> foreign key (artist_id) references artist(id),
...> foreign key (album_id) references album(id)
...> );

• Run ".schema" to see the existing tables.

Running the queries in the setup.sql file

• Run the queries in setup.sql for all the tables: track, artist_album, artist, and album. This will populate the tables:

INSERT INTO track (title, album_id) VALUES ("Super Awesome Track 1", 1); (and etc.)

• Create the other tables (album and artist):

create table album (
...> id integer primary key autoincrement,
...> title varchar(128),
...> release_year integer
...> );
create table artist (
...> id integer primary key autoincrement,
...> name varchar(128)
...> );

• And populate them:

INSERT INTO album (title, release_year) VALUES ("Super Awesome Album", 1990); (and etc.)

• If you need to delete any of the tables, run "drop table name_of_table".

Writing SQL "SELECT" queries

• Write SQL SELECT queries that show all albums:

select * from album;

• Show all albums made between 1975 and 1990:

select * from album where release_year >= 1975 and release_year < 1990;

• Show all albums whose names start with Super D:

select * from album where title like "Super D%";

• Show all albums that have no release year:

select * from album where release_year is null;

• Write SQL SELECT queries that show all track titles from Super Funky Album:

select track.title from track, album
...> where track.album_id = album.id and album.title = "Super Funky Album";

• Same query as above, but rename the column from title to Track_Title in the output.

select track.title as "Track Title" from track, album
...> where track.album_id = album.id and album.title = "Super Funky Album";

• Select all album titles by Han Solo:

select album.title from album, artist_album, artist
...> where artist_album.album_id = album.id and
...> artist_album.artist_id = artist.id and
...> artist.name = "Han Solo";

• Select the average year all albums were released:

select avg (release_year) from album;

• Select the average year all albums by Leia and the Ewoks were released:

select avg (release_year) from album, artist_album, artist
...> where artist_album.album_id = album.id and
...> artist_album.artist_id = artist.id and
...> artist.name = "Leia and the Ewoks";

• Select the number of artists:

select count (*) from artist;

• Select the number of tracks on Super Dubstep Album:

select count (*) from track, album
...> where track.album_id = album.id and
...> album.title = "Super Dubstep Album";

Day 2 Exercises

Note: SQLite doesn't enforce foreign key constrains by default. You have to enable them by running PRAGMA foreign_keys = ON; before your queries.

Create a database/table for taking notes.

• What are the columns that a note table needs?

create table notes (
...> id integer primary key autoincrement,
...> title varchar(128),
...> content varchar(128),
...> created_on datetime,
...> author_id integer,
...> foreign key(author_id) references author(id)
...> );

• If you have a timestamp field, how do you auto-populate it with the date?

INSERT INTO notes (created_on) VALUES (CURRENT_TIMESTAMP);

• A note should have a foreign key pointing to an author in an author table.
• Create a table for the authors. What columns are needed for the author table?

create table author (
...> id integer primary key autoincrement,
...> name varchar(128)
...> );

• Insert authors to the author table:

sqlite> insert into author (name) values ("Jane Austen");
sqlite> insert into author (name) values ("PG Wodehouse");
sqlite> insert into author (name) values ("Mortimer Adler");
sqlite> insert into author (name) values ("Anton Chekhov");

• Insert notes to the note table:

insert into notes (title, content, created_on, author_id) values ("Pride and Prejudice", "It is a truth universally acknowledged...", current_timestamp, 1);
sqlite> insert into notes (title, content, created_on, author_id) values ("Jeeves and Wooster", "Good morning, Jeeves!", current_timestamp, 2);
sqlite> insert into notes (title, content, created_on, author_id) values ("How to Read a Book", "In the case of books...", current_timestamp, 3);

• View the "notes" and "authors" tables:

select * from notes;
select * from authors;

• Select all notes by an author's name:

select title, content from notes, author
...> where notes.author_id = author.id and
...> author.name = "Jane Austen";

• Select author for a particular note by note ID:

select name from notes, author
...> where notes.author_id = author.id and
...> notes.id = 3;

• Select the names of all the authors along with the number of notes they each have. (Hint: GROUP BY.)

select name, count(*) from notes, author
...> where notes.author_id = author.id
...> group by author_id;

• Delete authors from the author table:

delete from author where id >= 4;

• Submit a file notes.sql with the queries that build (CREATE TABLE/INSERT) and query the database as noted above.