SQL Cheatsheet – Master the Essentials

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Whether you’re a beginner or brushing up, this concise guide covers the fundamentals of SQL.

You Should Know:

Basic SQL Commands with Practical Examples

-- SELECT data from a table 
SELECT  FROM users;

-- INSERT new data 
INSERT INTO users (name, email) VALUES ('Alice', '[email protected]');

-- UPDATE existing data 
UPDATE users SET email = '[email protected]' WHERE name = 'Alice';

-- DELETE data 
DELETE FROM users WHERE name = 'Alice';

Filtering Data

-- WHERE clause 
SELECT  FROM products WHERE price > 100;

-- BETWEEN 
SELECT  FROM orders WHERE order_date BETWEEN '2023-01-01' AND '2023-12-31';

-- LIKE (pattern matching) 
SELECT  FROM employees WHERE name LIKE 'A%'; -- Names starting with 'A'

-- IS NULL 
SELECT  FROM customers WHERE phone IS NULL;

Sorting & Aggregating Data

-- ORDER BY 
SELECT  FROM products ORDER BY price DESC;

-- COUNT, SUM, AVG, MIN, MAX 
SELECT COUNT() FROM orders; 
SELECT AVG(price) FROM products;

Joins in Action

-- INNER JOIN 
SELECT orders.id, customers.name 
FROM orders 
INNER JOIN customers ON orders.customer_id = customers.id;

-- LEFT JOIN (all orders, even without customers) 
SELECT orders.id, customers.name 
FROM orders 
LEFT JOIN customers ON orders.customer_id = customers.id;

Database & Table Management

-- CREATE TABLE 
CREATE TABLE employees ( 
id INT PRIMARY KEY, 
name VARCHAR(100) NOT NULL, 
salary DECIMAL(10, 2) 
);

-- ALTER TABLE (add a column) 
ALTER TABLE employees ADD COLUMN department VARCHAR(50);

-- CREATE INDEX (improve search performance) 
CREATE INDEX idx_customer_name ON customers(name);

Subqueries & Advanced Filtering

-- Subquery in WHERE 
SELECT name FROM products 
WHERE price > (SELECT AVG(price) FROM products);

-- Subquery in FROM 
SELECT avg_price.category 
FROM (SELECT category, AVG(price) as avg_price FROM products GROUP BY category) AS avg_price;

What Undercode Say

SQL remains a foundational skill for cybersecurity (SQL injection attacks), data analysis, and backend development. Mastering these commands helps in:
– Penetration Testing: Exploiting SQLi vulnerabilities.
– Forensics: Querying log databases.
– DevOps: Managing database backups (mysqldump, pg_dump).

Related Linux & Windows Commands

 Export MySQL data 
mysqldump -u root -p database_name > backup.sql

PostgreSQL query from CLI 
psql -U username -d dbname -c "SELECT  FROM users;"

SQLite operations 
sqlite3 mydb.db "SELECT  FROM logs;"

Windows SQLCMD 
sqlcmd -S server_name -U username -Q "SELECT @@VERSION"

Prediction

SQL will remain critical as databases evolve with AI-driven optimizations. Expect more natural language-to-SQL tools, but core querying skills will stay essential.

Expected Output:

A structured, executable SQL reference sheet for quick database operations.

For more SQL techniques, check SQLZoo or W3Schools SQL.

IT/Security Reporter URL:

Reported By: Aaronsimca Sql – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅

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