MySQL Cheat Sheet

Essential MySQL commands for connecting, writing SQL, managing indexes, and choosing storage engines and data types for reliable relational apps.

2 PagesIntermediateMar 5, 2026

Connecting & Basics

CLI connection and schema browsing.

sql

mysql -u root -pSHOW DATABASES;USE mydb;SHOW TABLES;DESCRIBE users;SOURCE dump.sql;   -- run a .sql file

SQL Essentials

Core DDL and DML statements.

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CREATE TABLE users (  id INT AUTO_INCREMENT PRIMARY KEY,  email VARCHAR(255) NOT NULL UNIQUE,  created_at DATETIME DEFAULT CURRENT_TIMESTAMP) ENGINE=InnoDB;INSERT INTO users (email) VALUES ('a@b.com');SELECT * FROM users WHERE email LIKE '%example%';UPDATE users SET email = 'x@y.com' WHERE id = 1;DELETE FROM users WHERE id = 1;

Indexes & EXPLAIN

Adding indexes and inspecting execution plans.

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CREATE INDEX idx_email ON users(email);ALTER TABLE users ADD INDEX idx_created (created_at);SHOW INDEX FROM users;EXPLAIN SELECT * FROM users WHERE email = 'a@b.com';

Storage Engines & Types

Engine choices and common column types.

InnoDB- default engine; supports transactions, foreign keys, row-level locking
MyISAM- legacy engine; no transactions, table-level locks only
VARCHAR(n)- variable-length string up to n characters
TEXT- large variable-length string, stored off-row
DECIMAL(p,s)- exact fixed-precision numeric type
JSON- native JSON column type with validation (5.7+)
ENUM- string restricted to a fixed, predefined list of values

Pro Tip

Stick with InnoDB (the default since 5.5) for new tables — it gives you row-level locking, foreign keys, and crash recovery, while MyISAM offers none of those and is effectively legacy.

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