An attempt at a simple sql problem for a job application

file_system.sql

#--#
#--# Database structure for Pretio
#--#
DROP TABLE IF EXISTS Folders;
DROP TABLE IF EXISTS Files;
DROP TABLE IF EXISTS Users;
DROP TABLE IF EXISTS Contents;

CREATE TABLE Users (
	userid Integer AUTO_INCREMENT,
	name varchar(255) NOT NULL,
	PRIMARY KEY(userid)
);

CREATE TABLE Files (
	userid Integer NOT NULL,
	fileid Integer AUTO_INCREMENT,
	name varchar(255) NOT NULL,
	url varchar(1024),
	PRIMARY KEY (fileid),
	FOREIGN KEY (userid) REFERENCES Users(userid)
);

CREATE TABLE Folders (
	userid Integer NOT NULL,
	folderid Integer AUTO_INCREMENT,
	name varchar(255) NOT NULL,
	PRIMARY KEY (folderid),
	FOREIGN KEY (userid) REFERENCES Users(userid)
);

CREATE TABLE Contents (
	contentid Integer AUTO_INCREMENT,
	parentid Integer,

	# the Folder or File (or User?)
	content Integer NOT NULL,

	PRIMARY KEY (contentid)
);

# Create 2 users
INSERT INTO Users (name)
VALUES ("Colton");
INSERT INTO Users (name)
VALUES ("Nicolas");

# Create an inaccessable File
INSERT INTO Files (userid, name, url)
VALUES (1 /*SELECT userid FROM Users WHERE name='Colton'*/, "ColtonFile", "http://www.coltonphillips.ca");

#Create an inaccessable Folder
INSERT INTO Folders(userid,name)
VALUES (2 /*SELECT userid FROM Users WHERE name='Colton'*/, "ColtonFolder");

#The ColtonFolder has no parent
INSERT INTO Contents(content,parentid)
VALUES (3 /*SELECT folderid FROM Folders WHERE name='ColtonFolder'*/, NULL);

#The ColtonFile is inside of the ColtonFolder
INSERT INTO Contents(content,parentid)
VALUES (4 /*SELECT fileid FROM Folders WHERE name='ColtonFile'*/
	,5 /*SELECT folderid FROM Folders WHERE name='ColtonFolder'*/);

# Display all users
select * from Users;

#Display Contents of a directory
select * from Contents where parentid=6 /*SELECT folderid FROM Folders WHERE name='ColtonFolder'*/;
select * from Contents;