Hey everyone! 👋

I’ve compiled a handy SQL Cheat Sheet to help you quickly reference key SQL commands and concepts. Whether you’re working with databases or just need a quick refresher, this guide has got you covered.

Let’s dive in!

🔗 Core Concepts

SQL: Structured Query Language for managing and manipulating relational databases.

📦 SQL Commands and Concepts

SELECT: Retrieves data from tables.

  SELECT * FROM employees;

INSERT: Adds new records to tables.

  INSERT INTO employees (name, position) VALUES ('John Doe', 'Developer');

UPDATE: Modifies existing records in tables.

  UPDATE employees SET position = 'Senior Developer' WHERE name = 'John Doe';

DELETE: Removes records from tables.

  DELETE FROM employees WHERE name = 'John Doe';

WHERE: Filters records based on conditions.

  SELECT * FROM employees WHERE position = 'Developer';

JOIN: Combines records from multiple tables.

  SELECT employees.name, departments.department_name
  FROM employees
  JOIN departments ON employees.department_id = departments.id;

INNER JOIN: Returns matching records from tables.

SELECT * FROM orders
INNER JOIN customers ON orders.customer_id = customers.id;

LEFT JOIN: Returns all left table records.

SELECT * FROM employees
LEFT JOIN departments ON employees.department_id = departments.id;

RIGHT JOIN: Returns all right table records.

SELECT * FROM employees
RIGHT JOIN departments ON employees.department_id = departments.id;

FULL JOIN: Returns all matching/non-matching records.

SELECT * FROM employees
FULL JOIN departments ON employees.department_id = departments.id;

GROUP BY: Groups rows sharing common fields.

  SELECT department_id, COUNT(*) as employee_count
  FROM employees
  GROUP BY department_id;

ORDER BY: Sorts records in ascending/descending order.

  SELECT * FROM employees ORDER BY name ASC;

HAVING: Filters groups after aggregation.

  SELECT department_id, COUNT(*) as employee_count
  FROM employees
  GROUP BY department_id
  HAVING COUNT(*) > 5;

DISTINCT: Removes duplicate records from results.

  SELECT DISTINCT department_id FROM employees;

LIMIT: Restricts the number of returned records.

  SELECT * FROM employees LIMIT 10;

OFFSET: Skips a specific number of records.

  SELECT * FROM employees LIMIT 10 OFFSET 20;

ALIAS: Renames tables or columns temporarily.

  SELECT name AS employee_name FROM employees;

UNION: Combines results of two SELECTs.

  SELECT name FROM employees
  UNION
  SELECT name FROM contractors;

INDEX: Speeds up data retrieval.

  CREATE INDEX idx_employee_name ON employees (name);

PRIMARY KEY: Uniquely identifies each table record.

  CREATE TABLE employees (
    id INT PRIMARY KEY,
    name VARCHAR(100)
  );

FOREIGN KEY: Links records between tables.

  CREATE TABLE orders (
    id INT PRIMARY KEY,
    customer_id INT,
    FOREIGN KEY (customer_id) REFERENCES customers(id)
  );

AUTO_INCREMENT: Automatically increments numeric values.

  CREATE TABLE employees (
    id INT AUTO_INCREMENT PRIMARY KEY,
    name VARCHAR(100)
  );

NOT NULL: Ensures column must have a value.

  CREATE TABLE employees (
    id INT PRIMARY KEY,
    name VARCHAR(100) NOT NULL
  );

DEFAULT: Sets default value for column.

  CREATE TABLE employees (
    id INT PRIMARY KEY,
    status VARCHAR(20) DEFAULT 'active'
  );

CHECK: Ensures column meets a condition.

  CREATE TABLE employees (
    id INT PRIMARY KEY,
    age INT CHECK (age >= 18)
  );

CONSTRAINT: Defines rules for table data integrity.

  ALTER TABLE employees
  ADD CONSTRAINT unique_name UNIQUE (name);

TRIGGER: Executes automatic actions on data changes.

  CREATE TRIGGER before_employee_insert
  BEFORE INSERT ON employees
  FOR EACH ROW
  BEGIN
    SET NEW.created_at = NOW();
  END;

VIEW: Virtual table based on a query.

  CREATE VIEW employee_view AS
  SELECT name, position FROM employees;

SUBQUERY: Nested query within another query.

  SELECT name FROM employees
  WHERE department_id IN (
    SELECT id FROM departments WHERE name = 'Sales'
  );

TRANSACTION: Ensures data consistency across operations.

  START TRANSACTION;
  UPDATE employees SET position = 'Manager' WHERE name = 'John Doe';
  COMMIT;

COMMIT: Saves all changes in a transaction.

  COMMIT;

ROLLBACK: Undoes changes in a transaction.

  ROLLBACK;

ACID: Ensures reliable database transactions (Atomicity, Consistency, Isolation, Durability).

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Feel free to reach out or follow me for more content on database management and SQL. Happy querying! 💻

📝 SQL Cheat Sheet for Developers

🔗 Core Concepts

📦 SQL Commands and Concepts

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