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-- Students who are 'guest' members and have no overdue books
SELECT name, membership_type
FROM library_members
WHERE membership_type = 'guest' AND has_overdue_books = 'no';

-- Members who are 'guest' or borrowed more than 3 books
SELECT name, number_of_books
FROM library_members
WHERE membership_type = 'guest' OR number_of_books > 3;

-- Exclude members who have overdue books
SELECT name
FROM library_members
WHERE NOT has_overdue_books = 'yes';

# Logical Operators

Logical operators allow you to **combine multiple conditions** in a SQL query using the `WHERE` clause. This helps you make your data filters more precise and powerful.

 

## Main Logical Operators

| Operator | Description | Example |
| -------- | ----------------------------------- | ---------------------------------------------------------- |
| `AND` | All conditions must be true | `membership_type = 'student' AND has_overdue_books = 'no'` |
| `OR` | At least one condition must be true | `membership_type = 'guest' OR number_of_books > 3` |
| `NOT` | Reverses or excludes a condition | `NOT has_overdue_books = 'yes'` |

 

## AND Operator Example

The `AND` operator is used to filter rows where all conditions must be true.

```sql title="Filter: Students with no overdue books"
SELECT name, membership_type
FROM library_members
WHERE membership_type = 'student' AND has_overdue_books = 'no';
```

This query returns students who do not have any overdue books.

 

## OR Operator Example

The `OR` operator is used to filter rows where at least one condition must be true.

```sql title="Filter: Guests or those with many books"
SELECT name, number_of_books
FROM library_members
WHERE membership_type = 'guest' OR number_of_books > 3;
```

This query returns either guests or anyone with more than 3 books checked out.

 

## NOT Operator Example

The `NOT` operator is used to filter rows where the condition is false.

```sql title="Filter: Exclude members with overdue books"
SELECT name
FROM library_members
WHERE NOT has_overdue_books = 'yes';
```

This query returns only members who do not have overdue books.

 

## Why It Matters

Logical operators are critical when:

* Applying multiple filters to a dataset
* Handling exceptions and special cases
* Writing queries that mirror real-world logic

They give you precise control over what data you retrieve.

 

## What’s Next?

In the next lesson, you’ll learn how to **sort and limit results** using `ORDER BY` and `LIMIT`.

This query returns all library members who do **not** have overdue books.

Operator	Description	Example
`AND`	All conditions must be true	`membership_type = 'student' AND has_overdue_books = 'no'`
`OR`	At least one condition must be true	`membership_type = 'guest' OR number_of_books > 3`
`NOT`	Reverses or excludes a condition	`NOT has_overdue_books = 'yes'`

Logical Operators

Main Logical Operators

AND Operator Example

OR Operator Example

NOT Operator Example

Why It Matters

What’s Next?

What does the following query do?