Data Filtering and Sorting

WHERE Clause

SELECT * FROM employees WHERE salary > 50000;

Comparison Operators

-- Equal
SELECT * FROM employees WHERE department = 'IT';

-- Not equal
SELECT * FROM employees WHERE department <> 'HR';

-- Range
SELECT * FROM employees WHERE salary BETWEEN 40000 AND 80000;

Logical Operators

-- AND
SELECT * FROM employees
WHERE department = 'IT' AND salary > 60000;

-- OR
SELECT * FROM employees
WHERE department = 'IT' OR department = 'Finance';

-- IN
SELECT * FROM employees
WHERE department IN ('IT', 'HR', 'Finance');

Pattern Matching

-- LIKE with wildcards
SELECT * FROM employees WHERE first_name LIKE 'J%';
SELECT * FROM employees WHERE email LIKE '%@gmail.com';

NULL Values

SELECT * FROM employees WHERE middle_name IS NULL;
SELECT * FROM employees WHERE middle_name IS NOT NULL;

ORDER BY

-- Ascending (default)
SELECT * FROM employees ORDER BY last_name;

-- Descending
SELECT * FROM employees ORDER BY salary DESC;

-- Multiple columns
SELECT * FROM employees ORDER BY department, salary DESC;

LIMIT/TOP

-- MySQL/PostgreSQL
SELECT * FROM employees ORDER BY salary DESC LIMIT 10;

-- SQL Server
SELECT TOP 10 * FROM employees ORDER BY salary DESC;