MySQL Cheat Sheet

Quick reference

This is a MySQL cheat sheet — the commands you use every day, in one place. Keep it handy while practising. Once these core patterns feel familiar, most real queries are just variations of them.

Databases and tables

SHOW DATABASES;
CREATE DATABASE shop;
USE shop;
SHOW TABLES;
CREATE TABLE items (id INT PRIMARY KEY AUTO_INCREMENT, name VARCHAR(50), price INT);
DESCRIBE items;
ALTER TABLE items ADD stock INT;
DROP TABLE items;

Insert, update, delete

INSERT INTO items (name, price) VALUES ('Pen', 10);
INSERT INTO items (name, price) VALUES ('Pen', 10), ('Book', 50);  -- many rows
UPDATE items SET price = 12 WHERE id = 1;
DELETE FROM items WHERE id = 1;

Always add a WHERE to UPDATE and DELETE, or every row is affected.

Selecting and filtering

SELECT * FROM items;
SELECT name, price FROM items;
SELECT * FROM items WHERE price > 20;
SELECT * FROM items WHERE name LIKE 'P%';
SELECT * FROM items WHERE price BETWEEN 10 AND 50;
SELECT DISTINCT name FROM items;
SELECT * FROM items ORDER BY price DESC LIMIT 5;

Joins

-- inner join (only matches)
SELECT o.id, c.name
FROM orders o JOIN customers c ON o.customer_id = c.id;

-- left join (all left rows, matched or not)
SELECT c.name, o.id
FROM customers c LEFT JOIN orders o ON o.customer_id = c.id;

Aggregates and grouping

SELECT COUNT(*) FROM items;
SELECT AVG(price), MAX(price), MIN(price), SUM(price) FROM items;
SELECT name, COUNT(*) FROM items GROUP BY name;
SELECT name, COUNT(*) FROM items GROUP BY name HAVING COUNT(*) > 1;

Use WHERE to filter rows, HAVING to filter groups after GROUP BY.

Handy functions

SELECT NOW(), CURDATE();
SELECT UPPER(name), LOWER(name), LENGTH(name) FROM items;
SELECT ROUND(price, 2), CEIL(price), FLOOR(price) FROM items;
SELECT IFNULL(stock, 0) FROM items;
SELECT CONCAT(name, ' - ', price) FROM items;

Summary

• Databases/tables: CREATE, USE, SHOW, DESCRIBE, ALTER, DROP.
• CRUD: INSERT, SELECT, UPDATE, DELETE (always WHERE for change).
• Filter with WHERE, LIKE, BETWEEN; sort with ORDER BY; cap with LIMIT.
• Join with JOIN ... ON; use LEFT JOIN to keep unmatched rows.
• Summarise with COUNT/SUM/AVG and GROUP BY / HAVING.

Next, practise these in SQL queries practice, or go deeper with 50 MySQL queries.