SQL Cheatsheet

SQL (Structured Query Language) is the standard language for working with relational databases. This cheatsheet covers the core statements.

Select

Read data from tables.

SELECT * FROM users;
SELECT name, email FROM users;
SELECT DISTINCT country FROM users;
SELECT name AS full_name FROM users;

Filtering

Narrow down rows with WHERE.

SELECT * FROM users WHERE age > 18;
SELECT * FROM users WHERE country = 'UK';
SELECT * FROM users WHERE name LIKE 'A%';
SELECT * FROM users WHERE id IN (1, 2, 3);
SELECT * FROM users WHERE age BETWEEN 18 AND 30;

Sorting & Limiting

Order and paginate results.

SELECT * FROM users ORDER BY created_at DESC;
SELECT * FROM users ORDER BY name ASC LIMIT 10;
SELECT * FROM users LIMIT 10 OFFSET 20;

Insert

Add new rows.

INSERT INTO users (name, email)
VALUES ('Ada', 'ada@example.com');

Update

Modify existing rows.

UPDATE users
SET name = 'Ada L.'
WHERE id = 1;

Delete

Remove rows.

DELETE FROM users WHERE id = 1;

Joins

Combine data across tables.

SELECT o.id, u.name
FROM orders o
INNER JOIN users u ON o.user_id = u.id;

SELECT u.name, o.id
FROM users u
LEFT JOIN orders o ON o.user_id = u.id;

Aggregation

Summarize data with GROUP BY.

SELECT country, COUNT(*) AS total
FROM users
GROUP BY country
HAVING COUNT(*) > 5;

SELECT AVG(age), MAX(age), MIN(age) FROM users;

Subqueries

Query within a query.

SELECT name FROM users
WHERE id IN (
  SELECT user_id FROM orders WHERE total > 100
);

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SQL is essential for any data-driven application. Master selects and joins first, then explore indexes, transactions, and window functions.

For full documentation, see https://www.postgresql.org/docs/