AND, OR, NOT Operators

So far, we have used the WHERE clause to filter data using a single condition. In real-world scenarios, one condition is usually not enough.

SQL provides logical operators — AND, OR, and NOT — to combine multiple conditions in a powerful and flexible way.

Why Do We Need Logical Operators?

Imagine you want to:

• Find employees who work in IT and earn more than 70,000
• Find employees who work in HR or Finance
• Exclude employees from a specific department

These scenarios are impossible with a single condition. That’s where logical operators come in.

The AND Operator

The AND operator returns rows only when all conditions are true.

Syntax:

SELECT *
FROM table_name
WHERE condition1 AND condition2;
  

Example: Employees in IT department earning more than 70,000.

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

Only employees who satisfy both conditions will be returned.

The OR Operator

The OR operator returns rows when at least one condition is true.

Syntax:

SELECT *
FROM table_name
WHERE condition1 OR condition2;
  

Example: Employees working in HR or Finance.

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

Rows matching either condition will appear in the result.

The NOT Operator

The NOT operator is used to exclude rows that match a condition.

Syntax:

SELECT *
FROM table_name
WHERE NOT condition;
  

Example: Employees not working in HR.

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

This query removes all HR employees from the result.

Combining AND, OR, NOT

Logical operators can be combined to build complex conditions.

Example: Employees in IT department earning more than 70,000 or employees in Finance.

SELECT name, department, salary
FROM employees
WHERE (department = 'IT' AND salary > 70000)
   OR department = 'Finance';
  

Parentheses () control the order of evaluation and make the logic clear.

Truth Table (Simple Logic)

Common Beginner Mistakes

• Forgetting parentheses in complex conditions
• Using AND when OR is needed (or vice versa)
• Assuming NOT removes columns instead of rows

When queries behave unexpectedly, always re-check your logic.

What’s Next?

In the next lesson, we will learn how to sort query results using the ORDER BY clause.