MySQL Database Management

Chapter 5: SQL Basics - SELECT, INSERT, UPDATE, DELETE

5.1 SELECT Queries

The SELECT statement retrieves data from tables.

-- Basic SELECT
SELECT * FROM users;

-- SELECT specific columns
SELECT id, username, email FROM users;

-- SELECT with WHERE clause
SELECT * FROM users WHERE id = 1;

-- SELECT with ORDER BY
SELECT * FROM users ORDER BY created_at DESC;

-- SELECT with LIMIT
SELECT * FROM users LIMIT 10;

5.2 INSERT Statements

INSERT adds new rows to tables.

-- Insert single row
INSERT INTO users (username, email, password_hash) 
VALUES ('john_doe', 'john@example.com', 'hashed_password');

-- Insert multiple rows
INSERT INTO users (username, email, password_hash) VALUES
('user1', 'user1@example.com', 'hash1'),
('user2', 'user2@example.com', 'hash2');

5.3 UPDATE Statements

UPDATE modifies existing data.

-- Update single row
UPDATE users SET email = 'newemail@example.com' WHERE id = 1;

-- Update multiple columns
UPDATE users 
SET email = 'newemail@example.com', updated_at = NOW() 
WHERE id = 1;

5.4 DELETE Statements

DELETE removes rows from tables.

-- Delete specific row
DELETE FROM users WHERE id = 1;

-- Delete with conditions
DELETE FROM users WHERE created_at < '2020-01-01';