feat(curriculum): add sql and bash review page (freeCodeCamp#61739)

Co-authored-by: Ilenia M <[email protected]>

Author: larymak

curriculum/challenges/english/blocks/review-bash-and-sql/6724e46581a1742244e45b59.md

@@ -7,8 +7,233 @@ dashedName: review-bash-and-sql
 
 # --description--
 
-Description placeholder
+## Database Normalization
 
-# --assignment--
+This is the process of organizing a relational database to reduce data redundancy and improve integrity.
+
+Its benefits include:
+
+- Minimizing duplicated data, which saves storage and reduces inconsistencies.
+- Enforcing data integrity through the use of primary and foreign keys.
+- Making databases easier to maintain and understand.
+
+### Normal Forms
+
+- **1NF (First Normal Form)**
+  - Each cell contains a single (atomic) value.
+  - Each record is unique (enforced by a primary key).
+  - Order of rows/columns is irrelevant.
+  - Example: Move multiple phone numbers from a `students` table into a separate `student_phones` table.
+
+- **2NF (Second Normal Form)**
+  - Meets 1NF requirements.
+  - No **partial dependencies**: every non-key attribute must depend on the entire composite primary key.
+  - Example: Split `orders` table into `order_header` and `order_items` to avoid attributes depending on only part of the key.
+
+- **3NF (Third Normal Form)**
+  - Meets 2NF requirements.
+  - No **transitive dependencies**: non-key attributes cannot depend on other non-key attributes.
+  - Example: Move `city_postal_code` to a `cities` table instead of storing it with every order.
+
+- **BCNF (Boyce-Codd Normal Form)**
+  - Meets 3NF requirements.
+  - Every determinant (left-hand side of a functional dependency) must be a superkey.
+
+**Tip**: Aim for 3NF in most designs for a good balance of integrity and performance.
+
+## Key SQL Concepts
+
+- SQL is a Structured Query Language for communicating with relational databases.
+- **Basic commands** → `SELECT`, `INSERT`, `UPDATE`, `DELETE`, `CREATE TABLE`, `ALTER TABLE`, etc.
+- `Joins` → Combines data from multiple tables (`INNER JOIN`, `LEFT JOIN`, `RIGHT JOIN`, `FULL JOIN`).
+
+## Running SQL Commands in Bash
+
+You can run SQL commands directly from the command line using the `psql` command-line client for PostgreSQL or similar tools for other databases.
+
+For example, to run a SQL file in PostgreSQL:
+
+```bash
+psql -U username -d database_name -c "SELECT * FROM students;"
+```
+
+You can also execute MySQL commands directly:
+
+```bash
+mysql -u username -p database_name -e "SELECT * FROM students;"
+```
+
+### Run SQL from a File
+
+```bash
+# PostgreSQL
+psql -U username -d database_name -f script.sql
+
+# MySQL
+mysql -u username -p database_name < script.sql
+```
+
+### Embed SQL in a Bash Script
+
+```bash
+#!/bin/bash
+DB_USER="school_admin"
+DB_NAME="school"
+
+# Insert student data
+psql -U "$DB_USER" -d "$DB_NAME" -c \
+"INSERT INTO students (name, age, major) VALUES ('Alice', 20, 'CS');"
+```
+
+### Use of Variables in SQL
+
+```bash
+#!/bin/bash
+DB_USER="school_admin"
+DB_NAME="school"
+STUDENT_NAME="Bob"
+AGE=21
+
+psql -U "$DB_USER" -d "$DB_NAME" -c \
+"INSERT INTO students (name, age) VALUES ('$STUDENT_NAME', $AGE);"
+```
+
+**Tip**: Sanitize variables to avoid SQL injection.
+
+## Retrieving and Using SQL Query Results in Bash
+
+When you run SQL queries via `psql`, you can **capture** and **process** the returned values in your Bash scripts.
+
+### Capturing a Single Value
+
+```bash
+#!/bin/bash
+DB_USER="school_admin"
+DB_NAME="school"
+
+# Get total student count
+STUDENT_COUNT=$(psql -U "$DB_USER" -d "$DB_NAME" -t -A -c \
+"SELECT COUNT(*) FROM students;")
+
+echo "Total students: $STUDENT_COUNT"
+```
+
+Output → 42
+
+### Retrieving Multiple Columns
 
-Review the Bash and SQL topics and concepts.
+```bash
+#!/bin/bash
+DB_USER="school_admin"
+DB_NAME="school"
+
+# Get top 3 students' names and ages
+RESULTS=$(psql -U "$DB_USER" -d "$DB_NAME" -t -A -F"," -c \
+"SELECT name, age FROM students LIMIT 3;")
+
+echo "Top 3 students:"
+echo "$RESULTS"
+```
+
+Output
+
+```bash
+Alice,20
+Bob,21
+Charlie,22
+```
+
+### Looping Through Query Results
+
+```bash
+#!/bin/bash
+DB_USER="school_admin"
+DB_NAME="school"
+
+# Get student names and majors
+psql -U "$DB_USER" -d "$DB_NAME" -t -A -F"," -c \
+"SELECT name, major FROM students;" | while IFS="," read -r name major
+do
+    echo "Student: $name | Major: $major"
+done
+```
+
+Shape of Output
+
+```bash
+Student: Alice | Major: CS
+Student: Bob   | Major: Math
+Student: Carol | Major: Physics
+```
+
+## SQL Injection
+
+It is a web security vulnerability where attackers insert malicious SQL code into input fields to manipulate the database.
+
+This can lead to risky actions like:
+
+- Bypassing authentication.
+- Stealing sensitive data.
+- Modifying or deleting records.
+
+An example of an SQL injection attack:
+
+```sql
+SELECT * FROM users WHERE username = ' " " OR "1"="1" -- ' AND password = 'anything';
+```
+
+This query would return all users because the condition `OR "1"="1"` is always true, allowing attackers to bypass login checks.
+
+### Preventing SQL Injection
+
+1. **Use Prepared Statements**: These separate SQL code from data, preventing injection. Here's an example (Node.js with pg):
+
+    ```sql
+    client.query('SELECT * FROM users WHERE username = $1 AND password = $2', [username, password]);
+    ```
+
+2. **Input Validation**: Sanitize and validate all user inputs to ensure they conform to expected formats.
+
+3. **Least Privilege**: Use database accounts with the minimum permissions necessary for the application.
+
+**Note**: Never grant admin rights to application accounts.
+
+## N+1 Problem
+
+The N+1 problem occurs when an application makes one query to retrieve a list of items (N) and then makes an additional query for each item to retrieve related data, resulting in N+1 queries.
+
+**Why It’s Bad**
+
+- Each query adds network and processing overhead.
+- Multiple small queries are slower than one optimized query.
+
+### Example of N+1 Pattern
+
+```sql
+-- 1: Get list of orders
+SELECT * FROM orders LIMIT 50;
+
+-- N: For each order, get customer
+SELECT * FROM customers WHERE customer_id = ...;
+```
+
+**Solution**: Use `JOINs` or other set-based operations.
+
+```sql
+SELECT 
+  orders.order_id,
+  orders.product,
+  orders.quantity,
+  customers.customer_id,
+  customers.name,
+  customers.email,
+  customers.address
+FROM orders
+JOIN customers 
+  ON orders.customer_id = customers.customer_id
+WHERE orders.order_id IN (SELECT order_id FROM orders LIMIT 50);
+```
+
+Always look for opportunities to combine related data into a single query.
+
+# --assignment--