Logical Operators: AND, OR, and NOT

Definition: Logical operators allow you to create more complex filters by combining two or more conditions or by reversing a condition. They are essential for narrowing down search results with high precision.

Usage: Beginner SQL course outlines introduce these operators early in filtering lessons because real-world data requests often involve multiple requirements, such as "Find active users (AND) who live in a specific region."

1. The AND Operator

The AND operator displays a record if all conditions separated by it are TRUE.

SELECT *
FROM students
WHERE age >= 18 AND city = 'Mysuru';

Effect: Only students who are at least 18 years old AND live in Mysuru will appear.

2. The OR Operator

The OR operator displays a record if any of the conditions separated by it are TRUE.

SELECT *
FROM students
WHERE city = 'Mysuru' OR city = 'Hassan';

Effect: Students from either Mysuru or Hassan will appear.

3. The NOT Operator

The NOT operator displays a record if the condition(s) is NOT TRUE (it reverses the logic).

SELECT *
FROM students
WHERE NOT age < 20;

Effect: This returns all students except those younger than 20 (functionally the same as age >= 20).

Operator Truth Table

Key Notes

• Order of Precedence: When you use multiple operators (e.g., AND and OR in the same line), SQL processes AND before OR. Use parentheses ( ) to force a different order and make your code more readable.
• Combining NOT: You will often see NOT used with other keywords, such as WHERE city NOT IN ('Bengaluru', 'Mysuru') or WHERE name NOT LIKE 'A%'.
• Readability: For simple logic, NOT age < 20 is less readable than age >= 20. Only use NOT when it makes the intent of the query clearer.