SmartNinja WD2

20180523_Create_a_database_Exercise41.md

Exercise 4.1 - Solutions:

Design

Create tables

-- Temporal.
CREATE TABLE User (
  Id INTEGER PRIMARY KEY
);

CREATE TABLE Employer (
  Id INTEGER PRIMARY KEY AUTOINCREMENT,
  Title TEXT,
  Phone TEXT,
  PhotoUrl TEXT
);

-- Companies must have a name.
CREATE TABLE Company (
  Id INTEGER PRIMARY KEY AUTOINCREMENT,
  EmployerId INTEGER,
  Name TEXT NOT NULL,
  LogoUrl TEXT,
  FOREIGN KEY('EmployerId') REFERENCES 'Employer'('Id')
);

-- Job Ads must have at least a job title.
CREATE TABLE Job (
  Id INTEGER PRIMARY KEY AUTOINCREMENT,
  CompanyId INTEGER,
  Title TEXT NOT NULL,
  Description TEXT,
  JobType TEXT,
  Region TEXT,
  FOREIGN KEY('CompanyId') REFERENCES 'Company'('Id')
);

-- MANY-TO-MANY relationship between Users & Jobs.
CREATE TABLE Application (
  Id INTEGER PRIMARY KEY AUTOINCREMENT,
  UserId INTEGER,
  JobId INTEGER,
  FOREIGN KEY('UserId') REFERENCES 'User'('Id'),
  FOREIGN KEY('JobId') REFERENCES 'Job'('Id')
);

-- Category tags for job ads, must have at least a name.
CREATE TABLE Category (
  Id INTEGER PRIMARY KEY AUTOINCREMENT,
  Name TEXT NOT NULL UNIQUE
);

-- MANY-TO-MANY relationship between Jobs & Category tags.
CREATE TABLE JobCategory (
  Id INTEGER PRIMARY KEY AUTOINCREMENT,
  JobId INTEGER,
  CategoryId INTEGER,
  FOREIGN KEY('JobId') REFERENCES 'Job'('Id'),
  FOREIGN KEY('CategoryId') REFERENCES 'Category'('Id')
);

-- SQLite cannot make a FK col with the ALTER command.
-- So, drop User and make a new one.
DROP TABLE User;
-- Actual User table.
CREATE TABLE User (
  Id INTEGER PRIMARY KEY AUTOINCREMENT,
  EmployerId INTEGER,
  Email TEXT NOT NULL UNIQUE,
  FirstName TEXT NOT NULL,
  LastName TEXT,
  FOREIGN KEY('EmployerId') REFERENCES 'Employer'('Id')
);

Add data

-- Add users.
INSERT INTO User (FirstName, LastName, Email, EmployerId)
VALUES ('Alicia', 'Wonderland', '[email protected]', NULL),
  ('Bob', 'Esponja', '[email protected]', NULL),
  ('Charlie', 'Brown', '[email protected]', NULL);

-- Add employers.
INSERT INTO Employer (Title, Phone, PhotoUrl)
VALUES ('CEO', '+34666777888', 'https://uinames.com/api/photos/male/1.jpg'),
  ('Director RRHH', '+34666555444', 'https://uinames.com/api/photos/male/2.jpg'),
  ('Head of HR', '+4470000000000', 'https://uinames.com/api/photos/male/3.jpg');

-- Add users who are employers.
INSERT INTO User (FirstName, LastName, Email, EmployerId)
VALUES ('Daniel', 'Travieso', '[email protected]', 1),
  ('Emilio', 'Electrónico', '[email protected]', 2),
  ('Félix', 'Rodríguez', '[email protected]', 3);

-- Add companies.
INSERT INTO Company (Name, LogoUrl, EmployerId)
VALUES ('Naughty Daniel Inc.', 'https://upload.wikimedia.org/wikipedia/commons/thumb/6/63/Signature_of_Prince_Daniel%2C_Duke_of_V%C3%A4sterg%C3%B6tland.PNG/320px-Signature_of_Prince_Daniel%2C_Duke_of_V%C3%A4sterg%C3%B6tland.PNG', 1),
  ('Unicorn Analytics SA', 'https://upload.wikimedia.org/wikipedia/commons/9/97/Logo_of_Unicorn_Analytics_company.jpg', 2),
  ('F-BOMB S.L.', 'https://s1.piq.land/2013/06/19/hskihtNhb0PcpSZTF2ImZ82N_400x400.png', 3);

-- Add job ads.
INSERT INTO Job ('CompanyId', 'Title', 'Description', 'JobType', 'Region')
VALUES (1, 'Janitor', 'We need a full-time janitor to take care of our giant reception hall.', 'Full-time', 'Murcia'),
  (2, 'FORTRAN & COBOL Developer', 'Unicorn Analytics is looking for a resilient genius who can code in both Fortran and Cobol, Delphy and Assembly experience is also mandatory. NOOBS NEED NOT APPLY!!', 'Full-time', 'World'),
  (3, 'Copywriter', 'F-BOMB SL necesita un copy que produzca insultos a cascoporro para nuestra app. Se valorará pertenencia a la RAE. Requisito imprescindible que el candidato/a tenga buenos modales y saber estar.', 'Student-job', 'Coín'),
  (3, 'Accountant', 'F-BOMB SL necesita un contable que cuente los insultos que recibimos en Twitter. Secundariamente hará la contabilidad de la empresa y el inventario anual.', 'Part-time', 'Coín');

-- Create categories.
INSERT INTO Category ('Name')
VALUES ('IT'), ('Advertising'), ('Maintenance'), ('Management'), ('Hardcore'),
  ('Spanish'), ('English'), ('Remote'), ('Journalism'), ('Accounting');

-- Tag job ads under categories.
INSERT INTO JobCategory ('JobId', 'CategoryId')
-- Janitor: #Maintenance.
VALUES (1, 3),
  -- Developer: #IT, #Hardcore, #Spanish, #English, #Remote.
  (2, 1), (2, 5), (2, 6), (2, 7), (2, 8),
  -- Copywriter: #Advertising, #Hardcore, #Spanish, #Journalism.
  (3, 2), (3, 5), (3, 6), (3, 9),
  -- Accountant: #Accounting.
  (4, 10);

-- Make job applications, 9 combinations plus accountant.
INSERT INTO Application ('UserId', 'JobId')
VALUES (1, 1), (1, 2), (1, 3),
       (2, 1), (2, 2), (2, 3),
       (3, 1), (3, 2), (3, 3),
       -- Bob applies to be an Accountant.
       (2, 4);

Make queries

How many jobs are in each of the regions?

-- Return jobs grouped by region.
SELECT Job.Region, COUNT(Job.Id) Jobs
FROM Job
GROUP BY Job.Region;

Output:

Region	Jobs
"Coín"	"2"
"Murcia"	"1"
"World"	"1"

Which company offers IT jobs?

-- Return companies offering IT jobs.
SELECT Company.Name, Jobs.CategoryName, Jobs.JobTitle
FROM (
  SELECT Job.CompanyId, Job.Title JobTitle, Category.Name CategoryName
  FROM Job
  INNER JOIN JobCategory ON Job.Id=JobCategory.JobId
  INNER JOIN Category ON Category.Id=JobCategory.CategoryId
  ) Jobs
INNER JOIN Company ON Company.Id=Jobs.CompanyId
WHERE Jobs.CategoryName='IT';

Output:

Company.Name	Jobs.CategoryName	Jobs.JobTitle
"Unicorn Analytics SA"	"IT"	"FORTRAN & COBOL Developer"

Who applied for an accountant?

-- Return users who applied for accountancy jobs.
SELECT User.FirstName FirstName, User.LastName LastName, Jobs.CategoryName
FROM (
  SELECT Job.Id JobId, Category.Name CategoryName
  FROM Job
  INNER JOIN JobCategory ON Job.Id=JobCategory.JobId
  INNER JOIN Category ON Category.Id=JobCategory.CategoryId
  ) Jobs
INNER JOIN User ON User.Id=Application.UserId
INNER JOIN Application ON Application.JobId=Jobs.JobId
WHERE Jobs.CategoryName='Accounting';

Output:

FirstName	LastName	Jobs.CategoryName
"Bob"	"Esponja"	"Accounting"

How many of the jobs are full-time jobs?

-- Return full-time jobs.
SELECT Job.Title, Job.JobType
FROM Job
WHERE Job.JobType='Full-time';

Output:

Title	JobType
"Janitor"	"Full-time"
"FORTRAN & COBOL Developer"	"Full-time"

---

BONUS QUERIES

Return a list of employers.

-- List employers.
SELECT User.FirstName, User.LastName, Employer.Title, Employer.Phone
FROM User
INNER JOIN Employer ON User.EmployerId=Employer.Id;

How can I get this project diagram, please