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SQL

Core SQL syntax for querying and modifying relational data.

Querying

SELECT name, email FROM users;
SELECT * FROM users WHERE age > 18;
SELECT * FROM users ORDER BY created_at DESC LIMIT 10;

Joins

SELECT orders.id, users.name
FROM orders
JOIN users ON users.id = orders.user_id;
  • JOIN / INNER JOIN — only matching rows.
  • LEFT JOIN — all rows from the left table, matched or not.

Aggregation

SELECT status, COUNT(*) FROM orders GROUP BY status;
SELECT AVG(price) FROM products WHERE category = 'books';

Modifying Data

INSERT INTO users (name, email) VALUES ('Ada', 'ada@example.com');
UPDATE users SET email = 'new@example.com' WHERE id = 1;
DELETE FROM users WHERE id = 1;

References

Related Cheat Sheets