SQL Cheatsheet: Essential Commands For Database Management

SQL (Structured Query Language) is the backbone of database operations. Below is a comprehensive cheatsheet covering core SQL commands, clauses, joins, functions, and table management.

Core SQL Commands

DDL (Data Definition Language)

CREATE TABLE employees (id INT, name VARCHAR(50)); 
DROP TABLE employees; 
ALTER TABLE employees ADD COLUMN salary DECIMAL(10,2); 
TRUNCATE TABLE employees; 
CREATE VIEW emp_view AS SELECT id, name FROM employees;

DML (Data Manipulation Language)

SELECT  FROM employees; 
INSERT INTO employees VALUES (1, 'John Doe', 5000.00); 
UPDATE employees SET salary = 6000.00 WHERE id = 1; 
DELETE FROM employees WHERE id = 1;

DCL (Data Control Language)

GRANT SELECT ON employees TO user1; 
REVOKE SELECT ON employees FROM user1;

DQL (Data Query Language)

SELECT name, salary FROM employees WHERE salary > 5000;

Clauses & Operators

SELECT  FROM employees WHERE salary BETWEEN 5000 AND 10000; 
SELECT name FROM employees WHERE name LIKE 'J%'; 
SELECT department, AVG(salary) FROM employees GROUP BY department HAVING AVG(salary) > 6000;

Joins

SELECT e.name, d.department_name FROM employees e INNER JOIN departments d ON e.dept_id = d.id; 
SELECT e.name, d.department_name FROM employees e LEFT JOIN departments d ON e.dept_id = d.id;

Functions

Aggregate Functions

SELECT COUNT() FROM employees; 
SELECT AVG(salary) FROM employees; 
SELECT MAX(salary), MIN(salary) FROM employees;

Window Functions

SELECT name, salary, RANK() OVER (ORDER BY salary DESC) AS rank FROM employees; 
SELECT name, salary, LAG(salary) OVER (ORDER BY id) AS prev_salary FROM employees;

Table Management

CREATE TABLE departments (id INT PRIMARY KEY, department_name VARCHAR(50)); 
ALTER TABLE employees ADD CONSTRAINT fk_dept FOREIGN KEY (dept_id) REFERENCES departments(id); 
TRUNCATE TABLE temp_data; 
DROP TABLE backup_employees;

Views

CREATE VIEW high_salary_employees AS SELECT  FROM employees WHERE salary > 7000; 
DROP VIEW high_salary_employees;

You Should Know:

SQL Injection Prevention

-- Use parameterized queries instead of string concatenation 
PREPARE stmt FROM 'SELECT  FROM users WHERE username = ? AND password = ?'; 
EXECUTE stmt USING @username, @password;

Backup & Restore (MySQL)

 Backup 
mysqldump -u root -p database_name > backup.sql

Restore 
mysql -u root -p database_name < backup.sql

PostgreSQL Commands

 Connect to PostgreSQL 
psql -U username -d database_name

List databases 
\l

List tables in current database 
\dt

SQLite Commands

 Open SQLite database 
sqlite3 database.db

Export to CSV 
sqlite3 -header -csv database.db "SELECT  FROM employees;" > employees.csv

Windows SQL Server (T-SQL)

-- Get all tables in a database 
SELECT table_name FROM information_schema.tables;

-- Backup database 
BACKUP DATABASE mydb TO DISK = 'C:\backup\mydb.bak';

What Undercode Say:

SQL remains a fundamental skill for database administrators, data analysts, and cybersecurity professionals. Mastering these commands enhances efficiency in querying, securing, and managing databases. Practice these in real-world scenarios, such as setting up a local MySQL instance or using SQLite for lightweight projects.

Expected Output:

A well-structured SQL reference sheet with executable commands for database operations, security best practices, and cross-platform database management.

Prediction:

As databases grow in complexity, SQL will continue evolving with AI-driven optimizations, automated query tuning, and tighter integration with cloud-native solutions. Learning advanced SQL (window functions, CTEs) will remain crucial for data professionals.

Relevant URLs:

IT/Security Reporter URL:

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

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