Query Language Snippets

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SQL Read
Filter records with set membership (IN).
SELECT * FROM products WHERE id IN (1, 2, 3);
SQL Read
Filter records with NULL check (IS NULL/IS NOT NULL).
SELECT * FROM customers WHERE email IS NULL;
SELECT * FROM customers WHERE email IS NOT NULL;
SQL Read
Limit and offset results (pagination).
SELECT * FROM users LIMIT 10 OFFSET 0;
SQL Read
Inner join two tables.
SELECT users.name, orders.amount FROM users INNER JOIN orders ON users.id = orders.user_id;
SQL Read
Left join two tables (include all rows from the left table).
SELECT users.name, orders.amount FROM users LEFT JOIN orders ON users.id = orders.user_id;
SQL Read
Right join two tables (include all rows from the right table).
SELECT users.name, orders.amount FROM users RIGHT JOIN orders ON users.id = orders.user_id;
SQL Read
Full outer join two tables (include all rows from both tables).
SELECT users.name, orders.amount FROM users FULL OUTER JOIN orders ON users.id = orders.user_id;
SQL Read
Group by and aggregate data (COUNT, AVG, SUM, etc.).
SELECT department, COUNT(*), AVG(salary) FROM employees GROUP BY department;
SQL Read
Subquery in WHERE clause.
SELECT name FROM employees WHERE salary > (SELECT AVG(salary) FROM employees);
SQL Read
Subquery with IN/EXISTS.
SELECT name FROM employees WHERE department_id IN (SELECT id FROM departments WHERE active = 1);
SQL Read
Use a window function (ROW_NUMBER, RANK, DENSE_RANK).
SELECT name, salary, RANK() OVER (ORDER BY salary DESC) as rank FROM employees;
SQL Read
Use a Common Table Expression (CTE) for complex queries.
WITH high_salary_employees AS (
  SELECT * FROM employees WHERE salary > 50000
)
SELECT * FROM high_salary_employees;