Ilias_Khugaev-w3-Databases

Week3/assignment/answers.md

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+1. **Which columns break 1NF?**
+- Each cell must have one single value (atomic).
+- No lists or repeated values in one cell.
+  <br>**These columns break 1NF:**
+<br>`food_code → example: C1, C2`
+<br>`food_description → example: Curry, Cake`
+
+
+2. **What entities can we extract?**
+   We can create 5 entities (tables):
+
+- Members → `people who join the dinner.`
+
+- Dinners → `dinner events.`
+
+- Venues → `places where dinners happen.`
+
+- Foods → `food items served.`
+
+Connections → who ate what, where, and when.
+
+3. **Name all the tables and columns that would make a 3NF compliant solution.**
+   - Members
+   `member_id	Primary Key`
+   `member_name	Text`
+   `member_address	Text`
+
+   - Dinners
+   `dinner_id	Primary Key`
+   `dinner_date	Date`
+   `venue_code	Foreign Key → Venues.venue_code`
+
+   - Venues
+   `venue_code	Primary Key`
+   `venue_description	Text`
+
+   - Foods
+   `food_code	Primary Key`
+   `food_description	Text`
+
+   - Member_Dinner
+   `member_id	Foreign Key → Members.member_id`
+   `dinner_id	Foreign Key → Dinners.dinner_id`
+

Week3/assignment/injection.js

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+// Give an example of a value that can be passed as name and code that would take advantage of SQL-injection and ( fetch all the records in the database)
+function getPopulation(Country, name, code, cb) {
+    // assuming that connection to the database is established and stored as conn
+    conn.query(
+        `SELECT Population FROM ${Country} WHERE Name = '${name}' and code = '${code}'`,
+        function (err, result) {
+            if (err) cb(err);
+            if (result.length == 0) cb(new Error("Not found"));
+            cb(null, result[0].name);
+        }
+    );
+}
+// we can pass name as ('' OR '1'='1), or code as ('' OR '1'='1)
+//  SELECT Population FROM Countries WHERE Name = '' OR '1'='1' and code = '' OR '1'='1';
+
+
+// Rewrite the function so that it is no longer vulnerable to SQL injection
+
+function getPopulation(Country, name, code, cb) {
+    conn.query(
+        `SELECT Population FROM ?? WHERE Name = ? AND code = ?`,
+        [Country, name, code],
+        function (err, result) {
+            if (err) return cb(err);
+            if (result.length === 0) return cb(new Error("Not found"));
+            cb(null, result[0].Population); // исправлено: result[0].name → result[0].Population
+        }
+    );
+}

Week3/assignment/package.json

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+{
+  "name": "assignment",
+  "version": "1.0.0",
+  "type": "module",
+  "main": "transactions-create-tables.js",
+  "scripts": {
+    "test": "echo \"Error: no test specified\" && exit 1"
+  },
+  "author": "",
+  "license": "ISC",
+  "description": "",
+  "dependencies": {
+    "mysql2": "^3.14.1"
+  }
+}

Week3/assignment/transaction.js

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+import mysql from 'mysql2/promise';
+
+const connection = await mysql.createConnection({
+    host: 'localhost',
+    user: 'hyfuser',
+    password : 'hyfpassword',
+});
+
+try {
+    await connection.query(`USE Transactions`)
+    await connection.query(`START TRANSACTION`);
+    await connection.query(`UPDATE account SET balance = balance - 1000 WHERE account_number = 1001`);
+    await connection.query(`UPDATE account SET balance = balance + 1000 WHERE account_number = 1002`);
+    await connection.query(`
+        INSERT INTO account_changes(account_number, amount, changed_date, remark)
+        VALUES
+            (1001, -1000, '2020-01-01', 'transaction'),
+            (1002, 1000, '2020-01-02', 'deposit')
+    `);
+    await connection.query(`COMMIT`);
+} catch (err) {
+    console.error("Transaction failed, rolling back:", err);
+    await connection.query(`ROLLBACK`);
+} finally {
+    connection.end();
+}

Week3/assignment/transactions-create-tables.js

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+import mysql from 'mysql2/promise';
+
+const connection = await mysql.createConnection({
+    host: 'localhost',
+    user: 'hyfuser',
+    password : 'hyfpassword',
+});
+
+try {
+    await  connection.query(`DROP DATABASE IF EXISTS Transactions`);
+    await connection.query(`CREATE DATABASE IF NOT EXISTS Transactions`);
+    await connection.query(`USE Transactions`)
+    await  connection.query(`CREATE TABLE IF NOT EXISTS account(
+        account_number INT  AUTO_INCREMENT PRIMARY KEY,
+        balance INT NOT NULL DEFAULT 0)`
+   );
+
+   await  connection.query(`CREATE TABLE IF NOT EXISTS account_changes(
+    change_number INT AUTO_INCREMENT PRIMARY KEY,
+    account_number INT,
+    amount INT, 
+    changed_date DATETIME,
+    remark TEXT,
+    FOREIGN KEY (account_number) REFERENCES account(account_number))`
+   );
+} catch (err) {
+    console.log(err);
+} finally {
+    connection.end();
+}

Week3/assignment/transactions-insert-values.js

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+import mysql from 'mysql2/promise';
+
+const connection = await mysql.createConnection({
+    host: 'localhost',
+    user: 'hyfuser',
+    password : 'hyfpassword',
+});
+
+try {
+    await  connection.query(`USE Transactions`);
+    await connection.query(`INSERT INTO account(account_number, balance)
+        VALUES (1001, 5000), 
+               (1002, 3000),
+               (1003, 7000)`
+    );
+    await  connection.query(`INSERT INTO account_changes(account_number, amount, changed_date, remark)
+    VALUES (1001, 1000, '2020-01-01', 'Initial deposit'), 
+           (1002, -1000, '2020-01-02', 'Initial deposit'),
+           (1003, 1000, '2020-01-03', 'Initial deposit')`
+    );
+} catch (err) {
+    console.log(err);
+} finally {
+    connection.end();
+}