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VladN-week1-Database #6

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c7e4161
Done 1st week
vlnach Aug 27, 2025
d59d114
Fixes for pull request
vlnach Sep 3, 2025
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149 changes: 149 additions & 0 deletions Week1/databases/ex1_meetup.js
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Original file line number Diff line number Diff line change
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require("dotenv").config();
const { Client } = require("pg");

// Admin connection (connects to default "postgres" DB)
// Used only for creating/dropping the "meetup" database
const adminConfig = {
host: process.env.PGHOST,
port: process.env.PGPORT,
user: process.env.PGUSER,
password: process.env.PGPASSWORD,
database: "postgres",
};

// Config to connect to the actual "meetup" DB
const meetupConfig = { ...adminConfig, database: "meetup" };

async function run() {
let admin; // reference to admin client
let db; // reference to meetup client
Comment on lines +18 to +19
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@yunchen4 yunchen4 Sep 5, 2025

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You can consider using just one instance of Client and do something like:

client.end();
client.database = "meetup";
client.connect();

This way the code will be more readable.

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@vlnach vlnach Sep 5, 2025

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Thank you! Next time will do it!


try {
// ================================
// 1. Reset the "meetup" database
// ================================
admin = new Client(adminConfig);
await admin.connect();

// Terminate active connections (safety measure)
await admin.query(`
SELECT pg_terminate_backend(pid)
FROM pg_stat_activity
WHERE datname = 'meetup' AND pid <> pg_backend_pid();
`);

// Drop and recreate the database
await admin.query(`DROP DATABASE IF EXISTS meetup;`);
await admin.query(`CREATE DATABASE meetup;`);

// Close admin connection (not needed anymore)
await admin.end();
admin = null;

// ================================
// 2. Connect to "meetup" database
// ================================
db = new Client(meetupConfig);
await db.connect();

// Drop old tables (if they exist, order matters because of FK dependencies)
await db.query(`DROP TABLE IF EXISTS Meeting;`);
await db.query(`DROP TABLE IF EXISTS Room;`);
await db.query(`DROP TABLE IF EXISTS Invitee;`);

// ================================
// 3. Create tables
// ================================

// Invitees table: list of people and who invited them
await db.query(`
CREATE TABLE Invitee (
invitee_no INTEGER GENERATED ALWAYS AS IDENTITY PRIMARY KEY,
invitee_name VARCHAR(100) NOT NULL,
invited_by VARCHAR(100) NOT NULL
);
`);

// Rooms table: meeting rooms with floor number
await db.query(`
CREATE TABLE Room (
room_no INTEGER GENERATED ALWAYS AS IDENTITY PRIMARY KEY,
room_name VARCHAR(100) NOT NULL,
floor_number SMALLINT NOT NULL,
CONSTRAINT room_floor_number_range CHECK (floor_number BETWEEN -5 AND 200)
);
`);

// Meetings table: references Room
await db.query(`
CREATE TABLE Meeting (
meeting_no INTEGER GENERATED ALWAYS AS IDENTITY PRIMARY KEY,
meeting_title VARCHAR(200) NOT NULL,
starting_time TIMESTAMPTZ NOT NULL,
ending_time TIMESTAMPTZ NOT NULL,
room_no INTEGER NOT NULL REFERENCES Room(room_no),
CONSTRAINT meeting_time_valid CHECK (ending_time > starting_time)
);
`);

// ================================
// 4. Seed data
// ================================

// Insert 5 invitees
await db.query(`
INSERT INTO Invitee (invitee_name, invited_by) VALUES
('Alice','Vlad'),
('Bob','Vlad'),
('Carol','Dima'),
('David','Dima'),
('Eve','Lena');
`);

// Insert 5 rooms and return generated IDs
const rooms = await db.query(`
INSERT INTO Room (room_name, floor_number) VALUES
('Amsterdam', 1),
('Rotterdam', 2),
('Utrecht', 3),
('Eindhoven', 2),
('Haarlem', 1)
RETURNING room_no;
`);

// Extract room_no values to bind in Meeting inserts
const r = rooms.rows.map((x) => x.room_no);

// Insert 5 meetings linked to the inserted rooms
await db.query(
`
INSERT INTO Meeting (meeting_title, starting_time, ending_time, room_no) VALUES
('Intro to Databases', '2025-08-27 10:00+00', '2025-08-27 11:00+00', $1),
('PostgreSQL Basics', '2025-08-27 12:00+00', '2025-08-27 13:00+00', $2),
('Schema Design', '2025-08-28 10:00+00', '2025-08-28 11:30+00', $3),
('SQL CRUD Practice', '2025-08-28 12:00+00', '2025-08-28 13:00+00', $4),
('Indexes & Performance', '2025-08-29 09:30+00', '2025-08-29 10:30+00', $5);
`,
r.slice(0, 5) // bind five room IDs
);

console.log(" Exercise 1: DONE (database, tables, and seed data inserted)");
} catch (err) {
console.error("Script failed:", err);
process.exitCode = 1; // do not force quit immediately, allow finally block
} finally {
// Ensure connections are closed even if error occurred
if (db) {
try {
await db.end();
} catch {}
}
if (admin) {
try {
await admin.end();
} catch {}
}
}
}

run();
140 changes: 140 additions & 0 deletions Week1/databases/ex2_world.js
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require("dotenv").config();
const { Client } = require("pg");

const worldConfig = {
host: process.env.PGHOST,
port: process.env.PGPORT,
user: process.env.PGUSER,
password: process.env.PGPASSWORD,
database: "world",
};

// Small helper to run a query and pretty-print up to 10 rows
async function q(db, label, sql, params = []) {
const res = await db.query(sql, params);
console.log(`\n=== ${label} ===`);
console.table(res.rows.slice(0, 10));
return res;
}

async function run() {
let db; // keep a reference so we can close it in finally

try {
db = new Client(worldConfig);
await db.connect();

// 1) Countries with population > 8M
await q(
db,
"Countries with population > 8M",
`SELECT name
FROM country
WHERE population > 8000000
ORDER BY population DESC;`
);

// 2) Countries that have "land" in their names
await q(
db,
'Countries with "land" in name',
`SELECT name
FROM country
WHERE name ILIKE '%land%'
ORDER BY name;`
);

// 3) Cities with population between 500k and 1M
await q(
db,
"Cities 500k..1M",
`SELECT name, population
FROM city
WHERE population BETWEEN 500000 AND 1000000
ORDER BY population DESC;`
);

// 4) Countries on the continent 'Europe'
await q(
db,
"Countries in Europe",
`SELECT name
FROM country
WHERE continent = 'Europe'
ORDER BY name;`
);

// 5) Countries by surface area (desc)
await q(
db,
"Countries by surface area (DESC)",
`SELECT name, surfacearea
FROM country
ORDER BY surfacearea DESC;`
);

// 6) Names of all cities in the Netherlands
await q(
db,
"Cities in the Netherlands",
`SELECT c.name
FROM city c
JOIN country co ON c.countrycode = co.code
WHERE co.name = 'Netherlands'
ORDER BY c.name;`
);

// 7) Population of Rotterdam
await q(
db,
"Population of Rotterdam",
`SELECT c.population
FROM city c
JOIN country co ON c.countrycode = co.code
WHERE co.name = 'Netherlands' AND c.name = 'Rotterdam';`
);

// 8) Top 10 countries by surface area
await q(
db,
"Top 10 countries by surface area",
`SELECT name, surfacearea
FROM country
ORDER BY surfacearea DESC
LIMIT 10;`
);

// 9) Top 10 most populated cities
await q(
db,
"Top 10 most populated cities",
`SELECT name, population
FROM city
ORDER BY population DESC
LIMIT 10;`
);

// 10) Estimated world population (sum of country populations)
await q(
db,
"World population (sum of countries.population)",
`SELECT SUM(population)::BIGINT AS world_population
FROM country;`
);

console.log("\n Exercise 2: DONE");
} catch (err) {
console.error(" Exercise 2 failed:", err);
// do not exit immediately; allow finally to close the connection
process.exitCode = 1;
} finally {
// always close the connection
if (db) {
try {
await db.end();
} catch {}
}
}
}

run();