🔗 SQL AND, OR, NOT – Combine Conditions Logically

🧲 Introduction – Why Use Logical Operators?

In SQL, logical operators like AND, OR, and NOT are used to combine multiple conditions in the WHERE clause. These operators help you build flexible, powerful, and precise queries.

Use them to:

• 🔍 Filter records using complex logic
• 🧠 Apply multiple checks in one query
• 🔁 Build layered conditions for decision making

🎯 In this guide, you’ll learn how to:

• Use AND to match multiple true conditions
• Use OR to match at least one condition
• Use NOT to exclude specific conditions
• Combine them together with parentheses

✅ 1. Using AND – All Conditions Must Be True

SELECT *
FROM employees
WHERE department = 'Sales' AND salary > 50000;

✅ Returns rows where both conditions are true.

🔁 2. Using OR – At Least One Condition is True

SELECT *
FROM customers
WHERE country = 'USA' OR country = 'Canada';

✅ Returns rows that match either of the two countries.

❌ 3. Using NOT – Negate a Condition

SELECT *
FROM users
WHERE NOT verified;

✅ Returns users who are not verified.

🧮 4. Combine AND, OR, and NOT

SELECT *
FROM employees
WHERE department = 'HR'
  AND (salary > 60000 OR experience > 10)
  AND NOT contract = 'temporary';

✅ Parentheses ensure logical grouping and avoid confusion.

📘 Best Practices

📌 Summary – Recap & Next Steps

Logical operators like AND, OR, and NOT allow you to write advanced WHERE conditions that match complex business rules.

🔍 Key Takeaways:

• AND requires all conditions to be true
• OR requires at least one condition to be true
• NOT inverts or excludes results
• Use parentheses to group conditions logically

⚙️ Real-World Relevance:
Used in search filters, fraud detection queries, report generation, and access control rules.

➡️ Next up: Explore SQL IN and BETWEEN for simplified multi-value conditions.

❓ FAQ – SQL AND, OR, NOT

❓ Can I use AND and OR together?

✅ Yes, but use parentheses to control the condition flow.

❓ What happens if I skip parentheses with AND/OR?

✅ SQL may evaluate them in the wrong order. Always group your logic.

❓ Is NOT the same as !=?

✅ No. NOT negates a whole condition, while != compares individual values.

❓ Can I nest multiple conditions?

✅ Yes, you can combine as many AND, OR, NOT as needed using proper grouping.

❓ Are these supported in all SQL databases?

✅ Yes, AND, OR, and NOT are part of standard SQL and supported everywhere.