IN THIS CHAPTER

• AND: both conditions must be true
• OR: at least one condition must be true
• NOT: invert a condition
• Parentheses to control evaluation order

IT employees earning > 70,000

SELECT name, department, salary 
FROM employees
WHERE department = 'IT' AND salary > 70000;

IT or HR employees

SELECT name, department 
FROM employees
WHERE department = 'IT' OR department = 'HR';

5.3 - NOT

Everyone except Salses

SELECT name, department 
FROM employees
WHERE NOT department = 'Sales';

5.4 - Parentheses - Always Be Explicit

❌ Common Mistake: AND has higher precedence than OR, just like multiplication vs addition in maths. WHERE a OR b AND c is evaluated as WHERE a OR (b AND c), which is almost never what you intended. Always use parentheses

Sales employees, OR IT employees earning > 80,000

SELECT name, department, salary 
FROM employees
WHERE department = 'Sales'
      OR (department = 'IT' AND salary > 80000);