📊 Basic Queries
SELECT * FROM employees -- Select all columns
SELECT name, salary FROM employees -- Select specific columns
SELECT * FROM employees WHERE salary > 50000 -- Filter with WHERE
SELECT * FROM employees ORDER BY salary DESC -- Sort results
📈 Aggregate Functions
SELECT COUNT(*) FROM employees -- Count rows
SELECT SUM(salary) FROM employees -- Sum values
SELECT AVG(salary) FROM employees -- Average value
SELECT department, COUNT(*) FROM employees GROUP BY department
SELECT department, AVG(salary) FROM employees GROUP BY department HAVING AVG(salary) > 50000
🔗 Set Operations
SELECT * FROM table1 UNION SELECT * FROM table2 -- Combine (unique)
SELECT * FROM table1 INTERSECT SELECT * FROM table2 -- Common rows
SELECT * FROM table1 EXCEPT SELECT * FROM table2 -- Difference
🔍 Nested Queries
SELECT * FROM employees WHERE salary > (SELECT AVG(salary) FROM employees)
SELECT * FROM employees WHERE department IN (SELECT department FROM departments WHERE location = 'NYC')