AND, OR, NOT logical operators in MySQL

Introduction

Logical operators help you combine or change conditions in database queries to get exactly the data you want.

Finding customers who live in a city AND have made a purchase.

Searching for products that are either in stock OR on sale.

Excluding employees who are NOT in the sales department.

Filtering orders that are from a specific date range AND have a high total.

Selecting users who are NOT admins OR have not logged in recently.

Syntax

MySQL

SELECT column_names FROM table_name WHERE condition1 AND condition2;
SELECT column_names FROM table_name WHERE condition1 OR condition2;
SELECT column_names FROM table_name WHERE NOT condition;

AND means both conditions must be true.

OR means at least one condition must be true.

NOT reverses the condition.

Examples

Finds employees who work in Sales and are currently active.

MySQL

SELECT * FROM employees WHERE department = 'Sales' AND status = 'Active';

Finds products that are either in stock or on sale.

MySQL

SELECT * FROM products WHERE stock > 0 OR on_sale = TRUE;

Finds users who are not admins.

MySQL

SELECT * FROM users WHERE NOT is_admin;

Sample Program

This creates a simple customers table, adds some data, then finds customers who live in New York and have made a purchase.

MySQL

CREATE TABLE customers (
  id INT,
  name VARCHAR(50),
  city VARCHAR(50),
  has_purchased BOOLEAN
);

INSERT INTO customers VALUES
(1, 'Alice', 'New York', TRUE),
(2, 'Bob', 'Los Angeles', FALSE),
(3, 'Carol', 'New York', FALSE),
(4, 'Dave', 'Chicago', TRUE);

SELECT name FROM customers WHERE city = 'New York' AND has_purchased = TRUE;

Important Notes

Use parentheses to group conditions when mixing AND and OR to avoid confusion.

NOT applies only to the condition immediately after it unless parentheses are used.

Summary

AND requires all conditions to be true.

OR requires at least one condition to be true.

NOT reverses the truth of a condition.

Practice

1. Which logical operator in MySQL requires all conditions to be true for the whole expression to be true?

easy

A. XOR

B. OR

C. NOT

D. AND

Solution

1. Step 1: Understand AND operator behavior

   The AND operator returns true only if every condition joined by it is true.

2. Step 2: Compare with other operators

   OR requires at least one true condition, NOT reverses truth, XOR is exclusive or.

3. Final Answer:

   AND -> Option D

4. Quick Check:

   AND means all true = A [OK]

Hint: AND means all conditions must be true [OK]

Common Mistakes:

• Confusing AND with OR
• Thinking NOT requires all true
• Mixing XOR with AND

2. Which of the following is the correct syntax to select rows where age is greater than 18 and status is 'active'?

easy

A. SELECT * FROM users WHERE age > 18 AND status = 'active';

B. SELECT * FROM users WHERE NOT age > 18 AND status = 'active';

C. SELECT * FROM users WHERE age > 18 OR status = 'active';

D. SELECT * FROM users WHERE age > 18 NOT status = 'active';

Solution

1. Step 1: Identify correct logical operator for both conditions

   We want rows where both age > 18 and status = 'active' are true, so use AND.

2. Step 2: Check syntax correctness

   SELECT * FROM users WHERE age > 18 AND status = 'active'; uses AND correctly and has valid SQL syntax.

3. Final Answer:

   SELECT * FROM users WHERE age > 18 AND status = 'active'; -> Option A

4. Quick Check:

   AND joins conditions correctly = C [OK]

Hint: Use AND to combine multiple true conditions [OK]

Common Mistakes:

• Using OR instead of AND
• Incorrect NOT placement
• Syntax errors like missing AND

3. Given the table employees with columns department and salary, what rows will this query return?

SELECT * FROM employees WHERE department = 'Sales' OR salary > 50000 AND NOT department = 'HR';

medium

A. Rows where department is 'Sales' or salary > 50000 or department is not 'HR'

B. Rows where department is 'Sales' and salary > 50000 and department is not 'HR'

C. Rows where department is 'Sales' or salary > 50000 and department is not 'HR'

D. Rows where salary > 50000 only

Solution

1. Step 1: Understand operator precedence

   AND has higher precedence than OR, so condition is: department = 'Sales' OR (salary > 50000 AND NOT department = 'HR').

2. Step 2: Interpret the conditions

   Rows match if department is 'Sales', or if salary > 50000 and department is not 'HR'.

3. Final Answer:

   Rows where department is 'Sales' or salary > 50000 and department is not 'HR' -> Option C

4. Quick Check:

   AND before OR, NOT reverses condition = B [OK]

Hint: AND binds tighter than OR; use parentheses to clarify [OK]

Common Mistakes:

• Ignoring operator precedence
• Misreading NOT placement
• Assuming OR applies to all conditions

4. Identify the error in this query:

SELECT * FROM orders WHERE NOT order_date > '2023-01-01' AND status = 'shipped' OR;

medium

A. Incorrect use of NOT operator

B. Missing condition after OR

C. AND should be OR

D. order_date comparison syntax error

Solution

1. Step 1: Check query syntax

   The query ends with OR but no condition follows it, causing syntax error.

2. Step 2: Verify other parts

   NOT and AND usage is correct; order_date comparison is valid.

3. Final Answer:

   Missing condition after OR -> Option B

4. Quick Check:

   OR must have two conditions = A [OK]

Hint: OR must always connect two conditions [OK]

Common Mistakes:

• Leaving OR without a following condition
• Misplacing NOT operator
• Confusing AND and OR usage

5. You want to select all customers who are NOT in the 'VIP' group AND have made a purchase OR have a balance greater than 1000. Which query correctly expresses this logic?

hard

A. SELECT * FROM customers WHERE NOT group = 'VIP' AND (purchases > 0 OR balance > 1000);

B. SELECT * FROM customers WHERE NOT (group = 'VIP' AND purchases > 0) OR balance > 1000;

C. SELECT * FROM customers WHERE NOT group = 'VIP' AND purchases > 0 OR balance > 1000;

D. SELECT * FROM customers WHERE NOT group = 'VIP' OR purchases > 0 AND balance > 1000;

Solution

1. Step 1: Translate the logic into conditions

   We want customers NOT in 'VIP' group AND (have purchases OR balance > 1000).

2. Step 2: Check operator precedence and parentheses

   AND has higher precedence than OR, so parentheses around (purchases > 0 OR balance > 1000) ensure correct grouping.

3. Step 3: Evaluate options

   SELECT * FROM customers WHERE NOT group = 'VIP' AND (purchases > 0 OR balance > 1000); correctly uses NOT on group, AND with grouped OR conditions. Others misplace parentheses or NOT.

4. Final Answer:

   SELECT * FROM customers WHERE NOT group = 'VIP' AND (purchases > 0 OR balance > 1000); -> Option A

5. Quick Check:

   NOT group, AND grouped OR = D [OK]

Hint: Use parentheses to group OR conditions with AND [OK]

Common Mistakes:

• Missing parentheses causing wrong logic
• Applying NOT to wrong part
• Confusing AND and OR precedence